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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	Apr. 30, 2018
Class of Stock [Line Items]
Entity Registrant Name	Bandwidth Inc.
Entity Central Index Key	0001514416
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Class A
Class of Stock [Line Items]
Entity Common Stock, Shares Outstanding		4,207,908
Common Class B
Class of Stock [Line Items]
Entity Common Stock, Shares Outstanding		13,508,378

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 38,773	$ 37,627
Marketable securities	8,492	0
Accounts receivable, net of allowance for doubtful accounts	24,404	21,225
Prepaid expenses and other current assets	6,953	6,400
Total current assets	78,622	65,252
Property and equipment, net	15,902	14,946
Intangible assets, net	7,478	7,643
Deferred costs, non-current	1,933	2,068
Other long-term assets	1,047	1,192
Goodwill	6,867	6,867
Deferred tax asset	3,915	6,526
Total assets	115,764	104,494
Current liabilities:
Accounts payable	3,154	3,025
Accrued expenses and other current liabilities	14,471	15,633
Current portion of deferred revenue and advanced billings	7,080	5,768
Current portion of long-term debt and capital lease obligations	67	92
Total current liabilities	24,772	24,518
Other liabilities	704	716
Deferred revenue, net of current portion	7,113	2,549
Total liabilities	32,589	27,783
Stockholders' equity:
Class A and Class B common stock	18	17
Additional paid-in capital	102,743	102,465
Accumulated deficit	(19,580)	(25,771)
Accumulated other comprehensive loss	(6)	0
Total stockholders’ equity	83,175	76,711
Total liabilities and stockholders’ equity	$ 115,764	$ 104,494

Condensed Consolidated Statements of Operations and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue	$ 53,012	$ 39,625
Cost of revenue	25,364	21,566
Gross profit	27,648	18,059
Operating expenses:
Research and development	3,781	2,682
Sales and marketing	4,522	2,558
General and administrative	10,569	7,637
Total operating expenses	18,872	12,877
Operating income	8,776	5,182
Other (expense) income, net	49	(421)
Income before income taxes	8,825	4,761
Income tax provision	(2,634)	(1,772)
Net income	6,191	2,989
Other comprehensive loss:
Change in unrealized net loss on marketable securities, net of income tax benefit of $0 and $2, respectively	(6)	0
Total comprehensive income	6,185	2,989
Net income	6,191	2,989
Less: net income allocated to participating securities	0	391
Net income attributable to common stockholders	$ 6,191	$ 2,598
Net income per share:
Basic (in usd per share)	$ 0.35	$ 0.22
Diluted (in usd per share)	$ 0.30	$ 0.20
Weighted average number of common shares outstanding:
Basic (in shares)	17,658,611	11,798,565
Diluted (in shares)	20,484,753	12,972,609

Condensed Consolidated Statements of Operations and Comprehensive Income - Parenthetical - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Income tax benefit	$ 2	$ 0

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net income	$ 6,191	$ 2,989
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization	1,387	1,376
Accretion of bond discount	(6)	0
Amortization of debt issuance costs	16	32
Stock-based compensation	493	246
Deferred taxes	2,611	1,562
Loss on disposal of property and equipment	9	9
Changes in operating assets and liabilities:
Accounts receivable	(3,179)	(166)
Prepaid expenses and other assets	(471)	(1,232)
Deferred costs	146	(401)
Accounts payable	(656)	(1,663)
Accrued expenses and other liabilities	(1,174)	(3,943)
Deferred revenue and advanced billings	5,876	222
Net cash (used in) provided by operating activities	11,243	(969)
Investing activities
Purchase of property and equipment	(961)	(130)
Capitalized software development costs	(441)	(677)
Purchase of marketable securities	(8,498)	0
Net cash used in investing activities	(9,900)	(807)
Financing activities
Borrowings on line of credit	0	4,000
Repayments on line of credit	0	(3,000)
Payments on capital leases	(25)	(15)
Repayments on term loan	0	(500)
Payment of costs related to the initial public offering	(285)	0
Proceeds from issuances of common stock	70	0
Proceeds from sale of fixed assets	0	3
Net cash provided by (used in) financing activities	(240)	488
Net (decrease) increase in cash, cash equivalents, and restricted cash	1,103	(1,288)
Cash, cash equivalents, and restricted cash, beginning of period	37,870	7,028
Cash, cash equivalents, and restricted cash, end of period	38,973	5,740
Supplemental disclosure of cash flow information
Cash paid during the year for interest	19	549
Cash (refunded) paid for taxes	90	(33)
Supplemental disclosure of noncash financing activities
Purchase of property and equipment, accrued but not paid	785	247
Unrealized loss on marketable securities, accrued but not realized	$ 6	$ 0

Organization and Description of Business	3 Months Ended
Organization and Description of Business	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business Bandwidth Inc. (together with its subsidiaries, “Bandwidth” or the “Company”) was founded in July 2000 and incorporated in Delaware on March 29, 2001. The Company’s headquarters are located in Raleigh, North Carolina. The Company is a cloud-based, software-powered communications platform-as-a-service (“CPaaS”) provider that enables enterprises to create, scale and operate voice or text communications services across any mobile application or connected device. The Company has two operating and reportable segments, CPaaS and Other. CPaaS revenue is derived from usage and monthly services fees charged for usage of Voice, Messaging, 911 and Phone Numbers solutions through the Company’s proprietary CPaaS software application programming interfaces. Other revenue consists of fees charged for services provided such as: SIP trunking, data resale, and a hosted Voice-over Internet Protocol (“VoIP”). The Other segment also includes revenue from traffic generated by other carriers, SMS registration fees and other miscellaneous product lines.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting. Certain information and disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Annual Report on Form 10-K filed with the SEC on February 26, 2018.

The condensed consolidated balance sheet as of December 31, 2017, included herein, was derived from the audited financial statements as of that date, but does not include all disclosures including certain notes required by GAAP on an annual reporting basis.

In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the financial position, results of operations, comprehensive income and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2018 or any future period.

Principles of Consolidation

The consolidated financial statements include the accounts of Bandwidth Inc. and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires the Company to make estimates and judgments that affect the amounts reported in these financial statements and accompanying notes. Although the Company believes that the estimates it uses are reasonable, due to the inherent uncertainty involved in making these estimates, actual results reported in future periods could differ from those estimates. These estimates in the consolidated financial statements include, but are not limited to, allowance for doubtful accounts, recoverability of long lived and intangible assets, customer relationship period, valuation allowances on tax assets, certain accrued expenses, and contingencies.

Cash and Cash Equivalents

The Company classifies all highly liquid investments with stated maturities of three months or less from date of purchase as cash equivalents and all highly liquid investments with stated maturities of greater than three months from the date of purchase as current marketable securities. The Company has a policy of making investments only with commercial institutions that have at least an investment grade credit rating. The Company invests its cash primarily in government securities and obligations, corporate debt securities, money market funds and reverse repurchase agreements (RRAs). RRAs are collateralized by deposits in the form of Government Securities and Obligations for an amount not less than 102% of their value. The Company does not record an asset or liability as the Company is not permitted to sell or repledge the associated collateral. The Company has a policy that the collateral has at least an "A" (or equivalent) credit rating. The Company utilizes a third party custodian to manage the exchange of funds and ensure that collateral received is maintained at 102% of the value of the RRAs on a daily basis. RRAs with stated maturities of greater than three months from the date of purchase are classified as marketable securities.

Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same such amounts shown in the condensed consolidated statements of cash flows:



	December 31,		March 31,
	2017		2018
Cash and cash equivalents	$	37,627	$	38,773
Restricted cash	243		200
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	37,870	$	38,973

Restricted cash is for Automated Clearing House availability, customer deposits and for credit card security. The Company has classified this asset as a long-term asset in order to match the expected period of restriction and is included in Other long-term assets in the condensed consolidated balance sheets.

Concentration of Credit Risk

Financial instruments that are exposed to concentration of credit risk consist primarily of cash and cash equivalents, marketable securities and trade accounts receivable. Cash deposits may be in excess of insured limits. The Company believes that the financial institutions that hold its cash deposits are financially sound and, accordingly, minimal credit risk exists with respect to these balances.

With regard to customers, credit evaluation and account monitoring procedures are used to minimize the risk of loss. The Company believes that no additional credit risk beyond amounts provided for by the allowance for doubtful accounts are inherent in accounts receivable. As of December 31, 2017, one customer represented approximately 13% of the Company's accounts receivable, net of allowance for doubtful accounts. As of March 31, 2018, one customer represented approximately 10% of the Company's accounts receivable, net of allowance for doubtful accounts.

For the three months ended March 31, 2017 and 2018, no individual customer represented more than 10% of the Company’s total revenue.

Recently Adopted Accounting Standards

In May 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-09, Compensation-Stock Compensation (Topic 718), Scope of Modification Accounting, which amends the scope of modification accounting for share-based payment arrangements. The ASU provides guidance on the types of changes to terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under ASC 718, Compensation-Stock Compensation. ASU 2017-09 is effective for fiscal years and interim periods within those years beginning after December 15, 2017. The adoption of this standard did not have a material impact on the Company's financial statements.

In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805) Clarifying the Definition of a Business, which amends the guidance of FASB Accounting Standards Codification Topic 805, “Business Combinations”, adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill, and consolidation. This guidance is effective for annual and interim periods beginning after December 15, 2017, and early adoption is permitted under certain circumstances. The impact from the adoption of this standard is dependent upon future transactions.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires a statement of cash flows to explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash and restricted cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017. The adoption of this standard did not have a material impact on the Company's financial statements.

In November 2016, the FASB issued ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. ASU 2016-16 requires companies to account for the income tax effects of intercompany transfers of assets other than inventory (e.g., intangible assets) when the transfer occurs. This guidance is effective for fiscal years beginning after December 15, 2017. The adoption of this standard did not have a material impact on the Company's financial statements.

In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows. The guidance also clarifies how the predominance principle should be applied when cash receipts and cash payments have aspects of more than one class of cash flows. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, and early adoption is permitted. The Company adopted this standard retrospectively and it had no material impact on the Company's financial statements.

Recent Accounting Pronouncements Not Yet Adopted

In February 2018, the FASB issued ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which addresses the income tax effects of items in accumulated other comprehensive income which were originally recognized in other comprehensive income, rather than in income from continuing operations. Specifically, it permits a reclassification from AOCI to retained earnings for the adjustment of deferred taxes due to the reduction of the historical corporate income tax rate to the newly enacted corporate income tax rate resulting from the U.S. tax law changes enacted in December 2017. This ASU is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The new guidance must be applied either on a prospective basis in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the U.S. tax law changes are recognized. The Company is evaluating the effect of adopting this new accounting guidance, but does not expect adoption will have a material impact on the Company’s financial statements.

In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, which simplifies the accounting for goodwill impairment. The ASU requires impairment charges to be based on the first step in today’s two-step impairment test. ASU 2017-04 is effective for annual and interim impairment tests performed in periods beginning after December 15, 2021, and early adoption is permitted. Management does not expect the adoption of this guidance to have a significant impact on the Company's financial position, results of operations, or cash flows.

In February 2016, the FASB issued ASU 2016-02, Leases. The standard will affect all entities that lease assets and will require lessees to recognize a lease liability and a right-of-use asset for all leases (except for short- term leases that have a duration of less than one year) as of the date on which the lessor makes the underlying asset available to the lessee. For lessors, accounting for leases is substantially the same as in prior periods. ASU 2016-02 is effective for fiscal years beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020, and early adoption is permitted. For leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, lessees and lessors must apply a modified retrospective transition approach. While the Company expects the adoption of this standard to result in an increase to the reported assets and liabilities, it has not yet determined the full impact the adoption of this standard will have on its financial statements and related disclosures.

In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers.” This new guidance will replace most existing GAAP guidance on this topic. The new revenue recognition standard provides a unified model to determine when and how revenue is recognized. The core principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration for which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14 “Revenue from Contracts with Customers: Deferral of the effective date,” which deferred by one year the effective date for the new revenue reporting standard for entities reporting under GAAP. In accordance with the deferral, this guidance will be effective for the Company beginning in the year ended December 31, 2019. This guidance can be applied either retrospectively to each period presented or as a cumulative effect adjustment as of the date of adoption. In December 2016, the FASB issued ASU 2016-20, “Revenue from Contracts with Customers, Technical Corrections and Improvements to Topic 606,” which made 12 additional technical corrections and improvements to the new revenue standard. In March 2016, the FASB issued ASU 2016-08, “Revenue from Contracts with Customers, Principal versus Agent Considerations (Reporting Revenue Gross versus Net)” clarifying the implementation guidance on principal versus agent considerations. Specifically, an entity is required to determine whether the nature of a promise is to provide the specified good or service itself (that is, the entity is a principal) or to arrange for the good or service to be provided to the customer by the other party (that is, the entity is an agent). The determination influences the timing and amount of revenue recognition. In April 2016, the FASB issued ASU 2016-10, “Revenue from Contracts with Customers, Identifying Performance Obligations and Licensing”, clarifying the implementation guidance on identifying performance obligations and licensing. Specifically, the amendments reduce the cost and complexity of identifying promised goods or services and improve the guidance for determining whether promises are separately identifiable. The amendments also provide implementation guidance on accounting for an entity’s promise to grant a license. In May 2016, the FASB issued ASU 2016-12, “Revenue from Contracts with Customers, Narrow-Scope Improvements and Practical Expedients,” clarifying guidance on assessing collectability, presentation of sales taxes, noncash consideration, completed contracts and contract modifications. The effective date and transition requirements for ASU 2016-20, ASU 2016-08 and ASU 2016-10 are the same as the effective date and transition requirements for ASU 2014-09, which will be effective for the Company beginning January 1, 2019.

The Company is still assessing all potential impacts of the new standard on its consolidated financial statements. Given the comprehensive nature of the standard, the Company has already taken steps to identify the impact on its consolidated financial results. The Company has completed a diagnostic which highlighted potential differences between current accounting policies and the new standard. Additionally, the Company has engaged a third-party service provider to assist in its evaluation of customer contracts to identify the attributes that could result in a different accounting treatment under ASU 2014-09. From an information technology perspective, the Company identified the preliminary business requirements and functionality of a new technology solution and has selected a software provider. The Company has not yet reached a conclusion as to whether the quantitative effect of the adoption of the new standard on its revenue will be material. The Company will continue to monitor and assess the impact of the changes of the new standard and the related interpretations of its application as they become available.

Fair Value of Financial Instruments

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

3. Fair Value of Financial Instruments

The carrying amounts of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses approximate fair value as of December 31, 2017 and March 31, 2018 because of the relatively short duration of these instruments. Marketable securities consist of U.S. treasury securities not otherwise classified as cash equivalents. All marketable securities are considered to be available-for-sale and are recorded at their estimated fair values. Unrealized gains and losses for available-for-sale securities are recorded in other comprehensive income (loss).

The Company evaluated its financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level in which to classify them for each reporting period. The following table summarizes the assets measured at fair value as of December 31, 2017 and March 31, 2018:



	Fair Value Measurements on a Recurring Basis December 31, 2017
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market account (included in cash and cash equivalents	$	28,015	$	—	$	—	$	28,015
Total financial assets	$	28,015	$	—	$	—	$	28,015

There were no marketable securities as of December 31, 2017.



	Amortized Cost or Carrying Value		Net Unrealized Losses			Fair Value Measurements on a Recurring Basis March 31, 2018
	Amortized Cost or Carrying Value		Net Unrealized Losses			Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:
Money market account	$	15,541	$	—		$	15,541	$	—	$	—	$	15,541
U.S. Reverse repurchase agreements	14,000		—			—		14,000		—		14,000
Total included in cash and cash equivalents	29,541		—			15,541		14,000		—		29,541
Marketable securities:
U.S. treasury securities	8,500		(8		)	—		8,492		—		8,492
Total marketable securities	8,500		(8		)	—		8,492		—		8,492
Total financial assets	$	38,041	$	(8	)	$	15,541	$	22,492	$	—	$	38,033

The Company classifies its marketable securities as current assets as they are available for current operating needs. The following table summarizes the contractual maturities of marketable securities as of March 31, 2018:



	Amortized Cost		Aggregate Fair Value
Financial Assets:
Less than one year	$	8,500	$	8,492
Total	$	8,500	$	8,492

For fixed income securities that had unrealized losses as of March 31, 2018, the Company determined that no other-than-temporary impairment existed. As of March 31, 2018, all securities in an unrealized loss position have been in an unrealized loss position for less than one year. During the three months ended March 31, 2018, there were no sales of marketable securities. Interest earned on marketable securities in the three months ended March 31, 2018 was $16 and is recorded as other (expense) income, net, in the accompanying condensed consolidated statements of operations and comprehensive income.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Financial Statement Components

3 Months Ended

Mar. 31, 2018

Financial Statement Components [Abstract]

Financial Statement Components

4. Financial Statement Components

Accounts receivable, net of allowance for doubtful accounts consist of the following:



	December 31,			March 31,
	2017			2018
Trade accounts receivable	$	44,692		$	15,002
Unbilled accounts receivable	8,653			10,335
Allowance for doubtful accounts	(32,463		)	(1,290		)
Other accounts receivable	343			357
Total accounts receivable, net	$	21,225		$	24,404

Components of allowance for doubtful accounts are as follows:



	Three Months Ended March 31,
Allowance for doubtful accounts:	2017			2018
Balance, beginning of period	$	255		$	189
Charged to bad debt expense	(43		)	1
Deductions (1)	(124		)	(48		)
Balance, end of period	$	88		$	142

________________________

(1) Write off of uncollectible accounts after all collection efforts have been exhausted.



	Three Months Ended March 31,
Allowance for CABS revenue:	2017			2018
Balance, beginning of period	$	22,316		$	32,274
Write-off of previously outstanding and fully reserved billings related to settlement	—			(24,968		)
Billings deemed not probable of collection (1)	2,463			118
Revenue recognized from outstanding billings previously deemed uncollectible related to settlement	—			(6,268		)
Deductions (2)	(43		)	(8		)
Balance, end of period	$	24,736		$	1,148

________________________

(1) Represents amounts billed in the period but where collectibility is not probable based on customers collection experience. Amounts were charged to a contra-revenue account.

(2) Write off of uncollectible accounts after all collection efforts have been exhausted.



	Three Months Ended March 31,
CABS revenue:	2017		2018
Billed	$	4,611	$	4,079
Revenue recognized from current billings (2)	2,148		3,961
Billings deemed not probable of collection (1)	$	2,463	$	118

________________________

(1) Represents amounts billed in the period but where collectibility is not probable based on customers collection experience. Amounts were charged to a contra-revenue account.

(2) Does not include $6,268 in revenue recognized as a result of a settlement agreement related to previously billed and outstanding and uncollectible invoices.

On January 29, 2018, the Company and Verizon entered into a settlement agreement to resolve an ongoing dispute and litigation with Verizon, which is a CABS customer of the Company. The settlement agreement also resolved Verizon’s counter-claims against the Company. Pursuant to the settlement agreement, Verizon made a lump sum payment to the Company on February 8, 2018 of $4,400, which was recognized as revenue during the three months ended March 31, 2018. Following receipt of the $4,400 payment, the Company issued to Verizon bill credits with respect to other CABS amounts previously billed to Verizon of $24,968, which were previously reserved and comprised the majority of the allowance for CABS revenue as of year-end. As of the three months ended March 31, 2018, the Company recognized as revenue $6,268, including the $4,400 payment made on February 8, 2018, in accounts receivable previously reserved for which collection is no longer in doubt. The settlement agreement also specifies certain terms for the Company's CABS billings to Verizon prospectively. The Company will continue to assess collectability of its outstanding CABS accounts receivable.

Accrued expenses and other current liabilities consisted of the following:



	December 31,		March 31,
	2017		2018
Accrued expense	$	6,851	$	7,878
Accrued compensation and benefits	5,237		2,809
Accrued sales, use, and telecom related taxes	3,030		3,146
Other accrued expenses	515		638
Total accrued expenses	$	15,633	$	14,471

Property and Equipment

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

Property and Equipment

5. Property and Equipment

Property and equipment, net consisted of the following:



	December 31,			March 31,
	2017			2018
Furniture and fixtures	$	863		$	872
Computer and office equipment	7,545			7,450
Telecommunications equipment	19,985			21,490
Leasehold improvements	453			453
Software development costs	15,517			16,073
Automobile	10			10
Total cost	44,373			46,348
Less—accumulated depreciation	(29,427		)	(30,446		)
Total property and equipment, net	$	14,946		$	15,902

The Company capitalized $677 and $441 of software development costs during the three months ended March 31, 2017 and 2018, respectively.

Amortization expense related to capitalized software development costs were $580 and $448 for the three months ended March 31, 2017 and 2018, respectively.

The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows:



	Three Months Ended March 31,
	2017		2018
Cost of revenue	$	1,047	$	1,064
Research and development	10		29
Sales and marketing	7		10
General and administrative	102		119
Total depreciation expense	$	1,166	$	1,222

Intangible Assets

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

6. Intangible Assets

Intangible assets consisted of the following as of December 31, 2017:



	Gross Amount		Accumulated Amortization			Net Carrying Value		Amortization Period
								(Years)
Customer relationships	$	10,396	$	(3,552	)	$	6,844	20
Domain name and related trademarks	2,678		(2,643		)	35		3–7
Licenses, amortizable	341		(341		)	—		2
Non-compete agreements	139		(139		)	—		2–5
Developed technology	775		(775		)	—		3
Licenses, indefinite lived	764		—			764		Indefinite
Total intangible assets, net	$	15,093	$	(7,450	)	$	7,643

Intangible assets consisted of the following as of March 31, 2018:



	Gross Amount		Accumulated Amortization			Net Carrying Value		Amortization Period
								(Years)
Customer relationships	$	10,396	$	(3,682	)	$	6,714	20
Domain name and related trademarks	2,678		(2,678		)	—		3–7
Licenses, amortizable	341		(341		)	—		2
Non-compete agreements	139		(139		)	—		2–5
Developed technology	775		(775		)	—		3
Licenses, indefinite lived	764		—			764		Indefinite
Total intangible assets, net	$	15,093	$	(7,615	)	$	7,478

Amortization expense for definite lived intangible assets was $210 and $165 for the three months ended March 31, 2017 and 2018, respectively. The weighted average amortization period for all definite lived intangible assets is 19 years.

Future estimated amortization expense for definite lived intangible assets subsequent to March 31, 2018 is as follows:



	Amount
2018 (remaining)	$	390
2019	520
2020	520
2021	520
2022	520
Thereafter	4,244
	$	6,714

Debt

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Debt

7. Debt

Revolving Loan

As of December 31, 2017 and March 31, 2018, the Company had $0 outstanding on the revolving loan and was in compliance with all financial and non-financial covenants for all periods presented. The available borrowing capacity under the revolving loan was $25,000 as of March 31, 2018.

As of December 31, 2017 and March 31, 2018, the outstanding unamortized loan fees for the revolving loan were $175 and $159, respectively, and are included in other long-term assets.

Capital Leases

The Company leases various equipment under leases accounted for as capital leases with expiration dates ranging from October 2018 through December 2018. As of December 31, 2017, cost and accumulated depreciation of the assets under capital leases recorded by the Company were $1,951 and $1,821, respectively. As of March 31, 2018, cost and accumulated depreciation of the assets under capital leases recorded by the Company were $1,951 and $1,863, respectively.

Remaining payments due on the Company’s capital lease obligations as of March 31, 2018, are as follows:



	Amount
2018 (remaining)	$	67
Less amount representing interest	—
	67
Less current maturities	67
	$	—

Segment and Geographic Information

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Segment and Geographic Information

8. Segment and Geographic Information

The Company has two reportable segments, CPaaS and Other. Segments are primarily evaluated based on revenue and gross profit. The Company does not allocate operating expenses, interest expense or income tax expense to its segments. Accordingly, the Company does not report such information. Additionally, the CODM does not evaluate the Company’s operating segments using discrete asset information. The segments share the majority of the Company’s assets. Therefore, no segment asset information is reported.



	Three Months Ended March 31,
	2017		2018
CPaaS
Revenue	$	31,647	$	38,897
Cost of revenue	18,228		21,905
Gross profit	$	13,419	$	16,992
Other
Revenue	$	7,978	$	14,115
Cost of revenue	3,338		3,459
Gross profit	$	4,640	$	10,656
Consolidated
Revenue	$	39,625	$	53,012
Cost of revenue	21,566		25,364
Gross profit	$	18,059	$	27,648

All assets were held in the United States as of December 31, 2017 and March 31, 2018.

The Company generates its revenue primarily in the United States. Revenue by geographical area is detailed in the table below (which is determined based on the customer billing address):



	Three Months Ended March 31,
	2017		2018
United States	$	39,518	$	52,824
International	107		188
Total	$	39,625	$	53,012

Stockholders' Equity

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

Stockholders' Equity

9. Stockholders’ Equity

Preferred Stock

As of December 31, 2017 and March 31, 2018, the Company had authorized 10,000,000 shares of undesignated preferred stock, par value $0.001, of which no shares were issued and outstanding.

Common Stock

As of December 31, 2017 and March 31, 2018, the Company had authorized 100,000,000 shares of Class A common stock with one vote per share and 20,000,000 shares of Class B common stock with ten votes per share, each par value $0.001. As of December 31, 2017, 4,197,831 and 13,440,724 shares of Class A and B common stock, respectively, were issued and outstanding. As of March 31, 2018, 4,202,831 and 13,489,628 shares of Class A and B common stock, respectively, were issued and outstanding.

Shares of Class B common stock are convertible into shares of Class A common stock upon the stockholder's voluntary written notice to the Company's transfer agent or a transfer by the stockholder, subject to limited exceptions for transfers for estate planning purposes.

The Company had reserved shares of common stock for issuance as follows:



	December 31,	March 31,
	2017	2018
Stock options issued and outstanding	3,659,791	3,658,999
Nonvested restricted stock units issued and outstanding	—	312,277
Stock purchase warrants issued and outstanding	51,350	—
Stock-based awards available for grant under the 2017 Plan	1,050,000	919,735
	4,761,141	4,891,011

Stock Based Compensation

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Based Compensation

10. Stock Based Compensation

2001 and 2010 Stock Option Plans

During 2001, the Company adopted the Bandwidth Inc. Stock Option Plan (the "2001 Plan"). As of July 26, 2010, the Company adopted the 2010 Equity Compensation Plan (the "2010 Plan").

Following the effectiveness of the 2010 Plan, the Company did not make any further grants under the 2001 Plan. However, the 2001 Plan continues to govern the terms and conditions of the outstanding awards granted under it. On November 9, 2017, the 2010 Plan was terminated in connection with the Company's IPO. Accordingly, no shares are available for future issuance under the 2010 Plan. However, the 2010 Plan continues to govern the terms and conditions of the outstanding awards granted thereunder.

2017 Incentive Award Plan

The Company's 2017 Incentive Award Plan (the "2017 Plan") became effective on November 9, 2017. The 2017 Plan provides for the grant of stock options, including incentive stock options and non-qualified stock options, stock appreciation rights, restricted stock, dividend equivalents, restricted stock units, and other stock or cash based awards to employees, consultants and directors of the Company. A total of 1,050,000 shares of the Company's Class A common stock were originally reserved for issuance under the 2017 Plan. These available shares automatically increase each January 1, beginning on January 1, 2018, by 5% of the number of shares of the Company's Class A common stock outstanding on the final day of the immediately preceding calendar year. On January 1, 2018, the shares available for grant under the 2017 Plan were automatically increased by 200,000 shares.

The terms of the stock option grants are determined by the Company’s Board of Directors. The Company’s stock options vest based on terms of the stock option agreements, which is generally over four years. The stock options have a contractual life of ten years.

RSUs granted under the 2017 Plan are subject to a time-based vesting condition. The compensation expense related to these awards is based on the grant date fair value of the RSUs and is recognized on a ratable basis over the applicable service period. The Company granted restricted stock units to its non-employee Board of Directors, some of which vested immediately while others vest 25% as of each calendar quarter immediately following the grant date. Other RSUs awarded to executives and employees are earned over a service period of four years.

Stock options

The fair value of options granted is estimated on the date of grant using the Black-Scholes option pricing model based on the assumptions in the table below:



	Three Months Ended March 31,
	2017	2018
Expected dividend yield	0%	0%
Expected stock price volatility	44%	47%
Average risk-free interest rate	2.0%-2.3%	2.5%
Expected life	6.2 years	6.2 years
Fair value of common stock	$9.60	$22.81

The following summarizes the stock option activity for the periods presented:



	Number of Options Outstanding		Weighted- Average Exercise Price (per share)		Weighted- Average Remaining Contract Life (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2017	3,659,791		$	6.88	4.38	$	59,436
Granted	17,988		22.81
Exercised	(5,000	)	6.74			$	111
Forfeited or cancelled	(13,780	)	12.19
Outstanding as of March 31, 2018	3,658,999		$	6.94	4.14	$	94,116

Options vested and exercisable at March 31, 2018	3,227,445		$	6.30	3.60	$	85,078

Options vested and expected to vest as of March 31, 2018	3,647,576		$	6.92	4.13	$	93,891

Aggregate intrinsic value represents the total pre-tax intrinsic value, which is computed based on the difference between the option exercise price and the estimated fair value of the Company’s common stock. Prior to the IPO, the fair value of the Company's common stock was estimated by the Company's board of directors. After the IPO, the fair value of the Company's common stock is the Company's Class A common stock price as reported on the NASDAQ Global Select Market.

The weighted average grant-date fair value of stock options granted was $4.34 and $11.10 for the three months ended March 31, 2017 and 2018, respectively.

The total estimated grant date fair value of options vested was $117 and $111 for the three months ended March 31, 2017 and 2018, respectively.

As of March 31, 2018, total unrecognized compensation cost related to all non-vested stock options was $1,869, which will be amortized over a weighted-average period of 2.55 years.

Restricted Stock Units

The following summarizes the restricted stock unit activity for the periods presented:



	Number of Awards Outstanding		Weighted-Average Grant Date Fair Value (per share)		Aggregate Intrinsic Value (in thousands)
Nonvested RSUs as of December 31, 2017	—		$	—	$	—
Granted	316,643		25.69
Vested	(4,046	)	22.81
Forfeited or cancelled	(320	)	28.58
Nonvested RSUs as of March 31, 2018	312,277		$	25.72	$	2,167

As of March 31, 2018, total unrecognized compensation cost related to non-vested RSUs was $7,874, which will be amortized over a weighted-average period of 3.85 years.

Stock-Based Compensation Expense

The Company recognized total stock-based compensation expense in continuing operations as follows:



	Three Months Ended March 31,
	2017		2018
Cost of revenue	$	20	$	18
Research and development	31		74
Sales and marketing	27		78
General and administrative	168		323
Total	$	246	$	493

Commitments and Contingencies

3 Months Ended

Mar. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

Operating Leases

The Company leases office space under operating lease agreements that expire at various dates beginning in 2021 and extend through 2025 in several locations within the United States including its headquarters, which is located in Raleigh, NC. On January 12, 2018, the Company entered into an 84 month operating lease agreement to provide 40,035 square feet of additional office space. This new lease is expected to commence in September 2018. On March 27, 2018, the Company entered into a 60 month operating lease agreement to provide 5,930 square feet of additional office space. This new lease is expected to commence in June 2018. The leases contain escalation clauses and various landlord concessions including a tenant improvement allowance. The Company recognizes the total minimum lease payments on a straight-line basis over the term of the lease.

Future minimum lease payments required under operating leases as of March 31, 2018 are as follows:



	Amount
2018 (remaining)	$	3,145
2019	5,004
2020	5,180
2021	5,254
2022	3,438
Thereafter	3,742
	$	25,763

The Company incurred rent expense of $513 and $933 for the three months ended March 31, 2017 and 2018, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations and comprehensive income.

On April 20, 2015, the Company created a wholly owned subsidiary, Republic Wireless, Inc. (“Republic”), which was incorporated in Delaware. On November 30, 2016, the Company completed a pro-rata distribution of the common stock of Republic to its stockholders of record as of the close of business (the “Spin-Off”).

In conjunction with the Spin-Off, the Company signed a Facilities Service Agreement with Republic in which the Company agreed to sub-lease 40,657 square feet of office space to Republic. The sub-lease is non-cancellable and extends to May 2022. The Company recorded a reduction of rent expense of $230 and $251 for the three months ended March 31, 2017 and 2018, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations and comprehensive income.

Future minimum sub-lease receipts required under the non-cancellable lease as of March 31, 2018 are as follows:



	Amount
2018 (remaining)	$	769
2019	1,042
2020	1,065
2021	1,089
2022	594
Thereafter	$	4,559

Contractual Obligations

On October 25, 2015, the Company entered into an agreement with a telecommunications service provider. The service agreement requires the Company to pay a monthly recurring charge beginning on January 1, 2016 associated with the services received. The service agreement is non-cancellable and contains annual minimum commitments of $1,200 to be fulfilled over five years or for as long as the Company continues to receive services from this vendor. In addition, the Company has other non-cancellable purchase obligations totaling $6,112 as of March 31, 2018, which consists primarily of non-cancellable or in-transit network equipment, which is expected to be received in less than one year.

Legal Matters

The Company is involved as a defendant in various lawsuits alleging that the Company failed to bill, collect and remit certain taxes and surcharges associated with the provision of 911 services pursuant to applicable laws in various jurisdictions. In August 2016, the Company received a Civil Investigative Demand from the Consumer Protection Division of the North Carolina Department of Justice, though no formal complaint has been filed in connection with that investigation. The North Carolina Department of Justice is investigating the billing, collection and remission of certain taxes and surcharges associated with 911 service pursuant to applicable laws of the State of North Carolina.

While the results of these legal proceedings cannot be predicted with certainty, in the opinion of management, the ultimate resolution of these matters will not have a material adverse effect on the Company’s financial position or results of operations.

On January 29, 2018, the Company and Verizon entered into a settlement agreement to resolve an ongoing dispute and litigation with Verizon, which is a CABS customer of the Company. The settlement agreement also resolved Verizon’s counter-claims against the Company. Pursuant to the settlement agreement, Verizon made a lump sum payment to the Company on February 8, 2018 of $4,400. Following receipt of the $4,400 payment, the Company issued to Verizon bill credits with respect to other CABS amounts previously billed to Verizon, which were previously reserved and comprised the majority of the allowance for CABS revenue as of year-end. The settlement agreement also specifies certain term for the Company's CABS billings to Verizon prospectively. The Company will continue to assess collectability of its outstanding CABS accounts receivable, including amounts due under this settlement agreement.

Employee Benefit Plan	3 Months Ended
Employee Benefit Plan	Mar. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plan	12. Employee Benefit Plan The Company sponsors a defined contribution 401(k) plan which allows eligible employees to defer a portion of their compensation. The Company, at its discretion, may make matching contributions. The Company made matching contributions of $351 and $287 for the three months ended March 31, 2017 and 2018, respectively.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes At the end of each interim reporting period, the Company determines the income tax provision by using an estimate of the annual effective tax rate, adjusted for discrete items occurring in the quarter. The Company’s effective tax rate was 37.2% and 29.8% for the three months ended March 31, 2017 and 2018, respectively. The change in tax rate is primarily due to the decrease in the federal statutory tax rate under the Tax Cuts and Jobs Act. The effective income tax rate reflects the effect of federal and state income taxes and the permanent impacts of differences in book and tax accounting. The Company’s effective tax rate for the three months ended March 31, 2018 differs from the U.S. federal statutory rate of 21.0% primarily due to state taxes, credits and other permanent differences. There has been no material change to the Company's SAB 118 assertion.

Related Parties	3 Months Ended
Related Parties	Mar. 31, 2018
Related Party Transactions [Abstract]
Related Parties	14. Related Parties In connection with the Spin-Off on November 30, 2016, the Company and Republic entered into certain agreements in order to govern the ongoing relationships between the two companies after the Spin-Off and to provide for an orderly transition. The agreements include a Transition Services Agreement, Facilities Sharing Agreement, Tax Sharing Agreement, and Master Services Agreement. The equity holders of Bandwidth pre-IPO are comprised of substantially the same individuals and entities that are the equity owners of Republic. The Company has determined the equity owners of Republic are related parties of Bandwidth. The Company has certain involvement with Republic via ongoing services arrangements, with these ongoing services arrangements creating a variable interest in Republic. The Company assessed the relationship with Republic under guidance for variable interest entities. Because investors in Republic have disproportionate voting rights, the Company concluded that Republic is a VIE, but Bandwidth is not a primary beneficiary. The Company’s maximum exposure to loss relating to this variable interest entity is limited to amounts due under the service agreements between the Company and Republic. For the three months ended March 31, 2017 and 2018, the Company received compensation of $351 and $28, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations and comprehensive income. In addition, there was approximately $15 and $11 due from Republic as of December 31, 2017 and March 31, 2018, respectively, which was recorded within accounts receivable in the accompanying condensed consolidated balance sheets. For the three months ended March 31, 2017 and 2018, the Company received rental payments under the Facilities Sharing Agreement of $230 and $251, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations and comprehensive income. No amounts were due to the Company under the Facilities Sharing Agreement as of December 31, 2017 and March 31, 2018. The Tax Sharing Agreement governs rights and obligations after the Spin-Off regarding income taxes and other taxes, including tax liabilities and benefits, attributes, returns and contests. There are no amounts outstanding or payable under this agreement as of December 31, 2017 and March 31, 2018. The Master Services Agreement specifies certain wholesale telecommunications services to be provided by the Company. The agreement is cancellable at any time by either party. During the three months ended March 31, 2017 and 2018, the Company provided telecommunication services to Republic of $534 and $986, respectively. The Company recognized such amounts as revenue in the accompanying condensed consolidated statements of operations and comprehensive income. As of December 31, 2017 and March 31, 2018, the Company had a receivable of $311 and $310, respectively, under the Master Services Agreement.

Basic and Diluted Income per Common Share

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Basic and Diluted Income per Common Share

15. Basic and Diluted Income per Common Share

As of December 31, 2017, the Company used the two-class method to compute net income per common share, because it had issued securities, other than common stock, that contractually entitled the holders to participate in dividends and earnings. These participating securities included the Company’s redeemable convertible preferred stock which had non-forfeitable rights to participate in any dividends declared on the Company’s common stock. The two-class method requires earnings for the period to be allocated between common stock and participating securities based upon their respective rights to receive distributed and undistributed earnings.

Under the two-class method, for periods with net income, basic net income per common share is computed by dividing the net income attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period. Net income attributable to common stockholders is computed by subtracting from net income the portion of current period earnings that the participating securities would have been entitled to receive pursuant to their dividend rights had all of the period’s earnings been distributed. No such adjustment to earnings is made during periods with a net loss, as the holders of the participating securities have no obligation to fund losses.

Diluted net income per common share is computed under the two-class method by using the weighted average number of shares of common stock outstanding, plus, for periods with net income attributable to common stockholders, the potential dilutive effects of stock options and warrants. The Company analyzed the potential dilutive effect of any outstanding dilutive securities under the “if-converted” method and treasury-stock method when calculating diluted earnings per share, in which it is assumed that the outstanding participating securities convert into common stock at the beginning of the period or date of issuance, if later. The Company reports the more dilutive of the approaches (two-class or “if-converted”) as its diluted net income per share during the period.

As of January 1, 2018, the Company no longer had outstanding securities other than common stock, which required holders' participation in dividends and earnings; therefore the Company no longer was required to calculate EPS under the two-class method. Basic net income per share is computed by dividing net income by the weighted-average number of shares of common stock outstanding during the period. Diluted net income per share is computed by giving effect to all potential shares of common stock, including stock options, stock related to unvested restricted stock awards, and outstanding warrants to the extent dilutive.

The components of basic and diluted earnings per share, or EPS, are as follows:



	Three Months Ended March 31,
	2017		2018
Earnings per share
Net income	$	2,989	$	6,191
Less: net income allocated to participating securities	391		—
Net income attributable to common stockholders	$	2,598	$	6,191
Net income per share:
Basic	$	0.22	$	0.35
Diluted	$	0.20	$	0.30
Weighted Average Number of Common Shares Outstanding
Basic	11,798,565		17,658,611
Dilutive effect of stock options, restricted stock units, and warrants	1,174,044		2,826,142
Diluted	12,972,609		20,484,753

The following common share equivalents have been excluded from the calculation of weighted-average common shares outstanding, because the effect is anti-dilutive for the periods presented:



	Three Months Ended March 31,
	2017	2018
Anti-dilutive Disclosure
Series A redeemable convertible preferred stock outstanding	1,775,000	—
Stock options issued and outstanding	588,365	94,126

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting. Certain information and disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Annual Report on Form 10-K filed with the SEC on February 26, 2018. The condensed consolidated balance sheet as of December 31, 2017, included herein, was derived from the audited financial statements as of that date, but does not include all disclosures including certain notes required by GAAP on an annual reporting basis. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the financial position, results of operations, comprehensive income and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2018 or any future period.
Principles of Consolidation	The consolidated financial statements include the accounts of Bandwidth Inc. and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires the Company to make estimates and judgments that affect the amounts reported in these financial statements and accompanying notes. Although the Company believes that the estimates it uses are reasonable, due to the inherent uncertainty involved in making these estimates, actual results reported in future periods could differ from those estimates. These estimates in the consolidated financial statements include, but are not limited to, allowance for doubtful accounts, recoverability of long lived and intangible assets, customer relationship period, valuation allowances on tax assets, certain accrued expenses, and contingencies.
Cash and Cash Equivalents	The Company classifies all highly liquid investments with stated maturities of three months or less from date of purchase as cash equivalents and all highly liquid investments with stated maturities of greater than three months from the date of purchase as current marketable securities. The Company has a policy of making investments only with commercial institutions that have at least an investment grade credit rating. The Company invests its cash primarily in government securities and obligations, corporate debt securities, money market funds and reverse repurchase agreements (RRAs). RRAs are collateralized by deposits in the form of Government Securities and Obligations for an amount not less than 102% of their value. The Company does not record an asset or liability as the Company is not permitted to sell or repledge the associated collateral. The Company has a policy that the collateral has at least an "A" (or equivalent) credit rating. The Company utilizes a third party custodian to manage the exchange of funds and ensure that collateral received is maintained at 102% of the value of the RRAs on a daily basis. RRAs with stated maturities of greater than three months from the date of purchase are classified as marketable securities.
Concentration of Credit Risk	Financial instruments that are exposed to concentration of credit risk consist primarily of cash and cash equivalents, marketable securities and trade accounts receivable. Cash deposits may be in excess of insured limits. The Company believes that the financial institutions that hold its cash deposits are financially sound and, accordingly, minimal credit risk exists with respect to these balances. With regard to customers, credit evaluation and account monitoring procedures are used to minimize the risk of loss. The Company believes that no additional credit risk beyond amounts provided for by the allowance for doubtful accounts are inherent in accounts receivable.
Recent Accounting Standards	Recently Adopted Accounting Standards In May 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-09, Compensation-Stock Compensation (Topic 718), Scope of Modification Accounting, which amends the scope of modification accounting for share-based payment arrangements. The ASU provides guidance on the types of changes to terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under ASC 718, Compensation-Stock Compensation. ASU 2017-09 is effective for fiscal years and interim periods within those years beginning after December 15, 2017. The adoption of this standard did not have a material impact on the Company's financial statements. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805) Clarifying the Definition of a Business, which amends the guidance of FASB Accounting Standards Codification Topic 805, “Business Combinations”, adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill, and consolidation. This guidance is effective for annual and interim periods beginning after December 15, 2017, and early adoption is permitted under certain circumstances. The impact from the adoption of this standard is dependent upon future transactions. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires a statement of cash flows to explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash and restricted cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017. The adoption of this standard did not have a material impact on the Company's financial statements. In November 2016, the FASB issued ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. ASU 2016-16 requires companies to account for the income tax effects of intercompany transfers of assets other than inventory (e.g., intangible assets) when the transfer occurs. This guidance is effective for fiscal years beginning after December 15, 2017. The adoption of this standard did not have a material impact on the Company's financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows. The guidance also clarifies how the predominance principle should be applied when cash receipts and cash payments have aspects of more than one class of cash flows. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, and early adoption is permitted. The Company adopted this standard retrospectively and it had no material impact on the Company's financial statements. Recent Accounting Pronouncements Not Yet Adopted In February 2018, the FASB issued ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which addresses the income tax effects of items in accumulated other comprehensive income which were originally recognized in other comprehensive income, rather than in income from continuing operations. Specifically, it permits a reclassification from AOCI to retained earnings for the adjustment of deferred taxes due to the reduction of the historical corporate income tax rate to the newly enacted corporate income tax rate resulting from the U.S. tax law changes enacted in December 2017. This ASU is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The new guidance must be applied either on a prospective basis in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the U.S. tax law changes are recognized. The Company is evaluating the effect of adopting this new accounting guidance, but does not expect adoption will have a material impact on the Company’s financial statements. In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, which simplifies the accounting for goodwill impairment. The ASU requires impairment charges to be based on the first step in today’s two-step impairment test. ASU 2017-04 is effective for annual and interim impairment tests performed in periods beginning after December 15, 2021, and early adoption is permitted. Management does not expect the adoption of this guidance to have a significant impact on the Company's financial position, results of operations, or cash flows. In February 2016, the FASB issued ASU 2016-02, Leases. The standard will affect all entities that lease assets and will require lessees to recognize a lease liability and a right-of-use asset for all leases (except for short- term leases that have a duration of less than one year) as of the date on which the lessor makes the underlying asset available to the lessee. For lessors, accounting for leases is substantially the same as in prior periods. ASU 2016-02 is effective for fiscal years beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020, and early adoption is permitted. For leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, lessees and lessors must apply a modified retrospective transition approach. While the Company expects the adoption of this standard to result in an increase to the reported assets and liabilities, it has not yet determined the full impact the adoption of this standard will have on its financial statements and related disclosures. In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers.” This new guidance will replace most existing GAAP guidance on this topic. The new revenue recognition standard provides a unified model to determine when and how revenue is recognized. The core principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration for which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14 “Revenue from Contracts with Customers: Deferral of the effective date,” which deferred by one year the effective date for the new revenue reporting standard for entities reporting under GAAP. In accordance with the deferral, this guidance will be effective for the Company beginning in the year ended December 31, 2019. This guidance can be applied either retrospectively to each period presented or as a cumulative effect adjustment as of the date of adoption. In December 2016, the FASB issued ASU 2016-20, “Revenue from Contracts with Customers, Technical Corrections and Improvements to Topic 606,” which made 12 additional technical corrections and improvements to the new revenue standard. In March 2016, the FASB issued ASU 2016-08, “Revenue from Contracts with Customers, Principal versus Agent Considerations (Reporting Revenue Gross versus Net)” clarifying the implementation guidance on principal versus agent considerations. Specifically, an entity is required to determine whether the nature of a promise is to provide the specified good or service itself (that is, the entity is a principal) or to arrange for the good or service to be provided to the customer by the other party (that is, the entity is an agent). The determination influences the timing and amount of revenue recognition. In April 2016, the FASB issued ASU 2016-10, “Revenue from Contracts with Customers, Identifying Performance Obligations and Licensing”, clarifying the implementation guidance on identifying performance obligations and licensing. Specifically, the amendments reduce the cost and complexity of identifying promised goods or services and improve the guidance for determining whether promises are separately identifiable. The amendments also provide implementation guidance on accounting for an entity’s promise to grant a license. In May 2016, the FASB issued ASU 2016-12, “Revenue from Contracts with Customers, Narrow-Scope Improvements and Practical Expedients,” clarifying guidance on assessing collectability, presentation of sales taxes, noncash consideration, completed contracts and contract modifications. The effective date and transition requirements for ASU 2016-20, ASU 2016-08 and ASU 2016-10 are the same as the effective date and transition requirements for ASU 2014-09, which will be effective for the Company beginning January 1, 2019. The Company is still assessing all potential impacts of the new standard on its consolidated financial statements. Given the comprehensive nature of the standard, the Company has already taken steps to identify the impact on its consolidated financial results. The Company has completed a diagnostic which highlighted potential differences between current accounting policies and the new standard. Additionally, the Company has engaged a third-party service provider to assist in its evaluation of customer contracts to identify the attributes that could result in a different accounting treatment under ASU 2014-09. From an information technology perspective, the Company identified the preliminary business requirements and functionality of a new technology solution and has selected a software provider. The Company has not yet reached a conclusion as to whether the quantitative effect of the adoption of the new standard on its revenue will be material. The Company will continue to monitor and assess the impact of the changes of the new standard and the related interpretations of its application as they become available.

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Reconciliation of Cash, Cash Equivalents, and Restricted Cash



	December 31,		March 31,
	2017		2018
Cash and cash equivalents	$	37,627	$	38,773
Restricted cash	243		200
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	37,870	$	38,973

Reconciliation of Cash, Cash Equivalents, and Restricted Cash



	December 31,		March 31,
	2017		2018
Cash and cash equivalents	$	37,627	$	38,773
Restricted cash	243		200
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	37,870	$	38,973

Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on a Recurring Basis

The following table summarizes the assets measured at fair value as of December 31, 2017 and March 31, 2018:



	Fair Value Measurements on a Recurring Basis December 31, 2017
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market account (included in cash and cash equivalents	$	28,015	$	—	$	—	$	28,015
Total financial assets	$	28,015	$	—	$	—	$	28,015

There were no marketable securities as of December 31, 2017.



	Amortized Cost or Carrying Value		Net Unrealized Losses			Fair Value Measurements on a Recurring Basis March 31, 2018
	Amortized Cost or Carrying Value		Net Unrealized Losses			Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:
Money market account	$	15,541	$	—		$	15,541	$	—	$	—	$	15,541
U.S. Reverse repurchase agreements	14,000		—			—		14,000		—		14,000
Total included in cash and cash equivalents	29,541		—			15,541		14,000		—		29,541
Marketable securities:
U.S. treasury securities	8,500		(8		)	—		8,492		—		8,492
Total marketable securities	8,500		(8		)	—		8,492		—		8,492
Total financial assets	$	38,041	$	(8	)	$	15,541	$	22,492	$	—	$	38,033

Schedule of Contractual Maturities of Marketable Securities

The following table summarizes the contractual maturities of marketable securities as of March 31, 2018:



	Amortized Cost		Aggregate Fair Value
Financial Assets:
Less than one year	$	8,500	$	8,492
Total	$	8,500	$	8,492

Financial Statement Components (Tables)

3 Months Ended

Mar. 31, 2018

Financial Statement Components [Abstract]

Schedule of Accounts Receivable, CABS Revenue and Allowance for Doubtful Accounts

Components of allowance for doubtful accounts are as follows:



	Three Months Ended March 31,
Allowance for doubtful accounts:	2017			2018
Balance, beginning of period	$	255		$	189
Charged to bad debt expense	(43		)	1
Deductions (1)	(124		)	(48		)
Balance, end of period	$	88		$	142

________________________

(1) Write off of uncollectible accounts after all collection efforts have been exhausted.



	Three Months Ended March 31,
Allowance for CABS revenue:	2017			2018
Balance, beginning of period	$	22,316		$	32,274
Write-off of previously outstanding and fully reserved billings related to settlement	—			(24,968		)
Billings deemed not probable of collection (1)	2,463			118
Revenue recognized from outstanding billings previously deemed uncollectible related to settlement	—			(6,268		)
Deductions (2)	(43		)	(8		)
Balance, end of period	$	24,736		$	1,148

________________________

(1) Represents amounts billed in the period but where collectibility is not probable based on customers collection experience. Amounts were charged to a contra-revenue account.

(2) Write off of uncollectible accounts after all collection efforts have been exhausted.



	Three Months Ended March 31,
CABS revenue:	2017		2018
Billed	$	4,611	$	4,079
Revenue recognized from current billings (2)	2,148		3,961
Billings deemed not probable of collection (1)	$	2,463	$	118

________________________

(1) Represents amounts billed in the period but where collectibility is not probable based on customers collection experience. Amounts were charged to a contra-revenue account.

(2) Does not include $6,268 in revenue recognized as a result of a settlement agreement related to previously billed and outstanding and uncollectible invoices

Accounts receivable, net of allowance for doubtful accounts consist of the following:



	December 31,			March 31,
	2017			2018
Trade accounts receivable	$	44,692		$	15,002
Unbilled accounts receivable	8,653			10,335
Allowance for doubtful accounts	(32,463		)	(1,290		)
Other accounts receivable	343			357
Total accounts receivable, net	$	21,225		$	24,404

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:



	December 31,		March 31,
	2017		2018
Accrued expense	$	6,851	$	7,878
Accrued compensation and benefits	5,237		2,809
Accrued sales, use, and telecom related taxes	3,030		3,146
Other accrued expenses	515		638
Total accrued expenses	$	15,633	$	14,471

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment, Net

The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows:



	Three Months Ended March 31,
	2017		2018
Cost of revenue	$	1,047	$	1,064
Research and development	10		29
Sales and marketing	7		10
General and administrative	102		119
Total depreciation expense	$	1,166	$	1,222

Property and equipment, net consisted of the following:



	December 31,			March 31,
	2017			2018
Furniture and fixtures	$	863		$	872
Computer and office equipment	7,545			7,450
Telecommunications equipment	19,985			21,490
Leasehold improvements	453			453
Software development costs	15,517			16,073
Automobile	10			10
Total cost	44,373			46,348
Less—accumulated depreciation	(29,427		)	(30,446		)
Total property and equipment, net	$	14,946		$	15,902

Summary of Depreciation Expense

The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows:



	Three Months Ended March 31,
	2017		2018
Cost of revenue	$	1,047	$	1,064
Research and development	10		29
Sales and marketing	7		10
General and administrative	102		119
Total depreciation expense	$	1,166	$	1,222

Property and equipment, net consisted of the following:



	December 31,			March 31,
	2017			2018
Furniture and fixtures	$	863		$	872
Computer and office equipment	7,545			7,450
Telecommunications equipment	19,985			21,490
Leasehold improvements	453			453
Software development costs	15,517			16,073
Automobile	10			10
Total cost	44,373			46,348
Less—accumulated depreciation	(29,427		)	(30,446		)
Total property and equipment, net	$	14,946		$	15,902

Intangible Assets (Tables)

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Intangible Assets

Intangible assets consisted of the following as of December 31, 2017:



	Gross Amount		Accumulated Amortization			Net Carrying Value		Amortization Period
								(Years)
Customer relationships	$	10,396	$	(3,552	)	$	6,844	20
Domain name and related trademarks	2,678		(2,643		)	35		3–7
Licenses, amortizable	341		(341		)	—		2
Non-compete agreements	139		(139		)	—		2–5
Developed technology	775		(775		)	—		3
Licenses, indefinite lived	764		—			764		Indefinite
Total intangible assets, net	$	15,093	$	(7,450	)	$	7,643

Intangible assets consisted of the following as of March 31, 2018:



	Gross Amount		Accumulated Amortization			Net Carrying Value		Amortization Period
								(Years)
Customer relationships	$	10,396	$	(3,682	)	$	6,714	20
Domain name and related trademarks	2,678		(2,678		)	—		3–7
Licenses, amortizable	341		(341		)	—		2
Non-compete agreements	139		(139		)	—		2–5
Developed technology	775		(775		)	—		3
Licenses, indefinite lived	764		—			764		Indefinite
Total intangible assets, net	$	15,093	$	(7,615	)	$	7,478

Schedule of Future Estimated Amortization Expense

Future estimated amortization expense for definite lived intangible assets subsequent to March 31, 2018 is as follows:



	Amount
2018 (remaining)	$	390
2019	520
2020	520
2021	520
2022	520
Thereafter	4,244
	$	6,714

Debt (Tables)

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Schedule of Remaining Payments due on Capital Lease Obligations

Remaining payments due on the Company’s capital lease obligations as of March 31, 2018, are as follows:



	Amount
2018 (remaining)	$	67
Less amount representing interest	—
	67
Less current maturities	67
	$	—

Segment and Geographic Information (Tables)

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment



	Three Months Ended March 31,
	2017		2018
CPaaS
Revenue	$	31,647	$	38,897
Cost of revenue	18,228		21,905
Gross profit	$	13,419	$	16,992
Other
Revenue	$	7,978	$	14,115
Cost of revenue	3,338		3,459
Gross profit	$	4,640	$	10,656
Consolidated
Revenue	$	39,625	$	53,012
Cost of revenue	21,566		25,364
Gross profit	$	18,059	$	27,648

Schedule of Revenue by Geographical Area

The Company generates its revenue primarily in the United States. Revenue by geographical area is detailed in the table below (which is determined based on the customer billing address):



	Three Months Ended March 31,
	2017		2018
United States	$	39,518	$	52,824
International	107		188
Total	$	39,625	$	53,012

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

Schedule of Reserved Shares of Common Stock for Issuance

The Company had reserved shares of common stock for issuance as follows:



	December 31,	March 31,
	2017	2018
Stock options issued and outstanding	3,659,791	3,658,999
Nonvested restricted stock units issued and outstanding	—	312,277
Stock purchase warrants issued and outstanding	51,350	—
Stock-based awards available for grant under the 2017 Plan	1,050,000	919,735
	4,761,141	4,891,011

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65877616&loc=d3e177068-122764

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(d))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21553-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Subparagraph (SX 210.5-02(28))
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65888546&loc=d3e21300-112643

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21484-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21488-112644

+ Details

Stock Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Fair Value of Options Granted Using the Black-Scholes Pricing Model

The fair value of options granted is estimated on the date of grant using the Black-Scholes option pricing model based on the assumptions in the table below:



	Three Months Ended March 31,
	2017	2018
Expected dividend yield	0%	0%
Expected stock price volatility	44%	47%
Average risk-free interest rate	2.0%-2.3%	2.5%
Expected life	6.2 years	6.2 years
Fair value of common stock	$9.60	$22.81

Summary of Stock Option Activity

The following summarizes the stock option activity for the periods presented:



	Number of Options Outstanding		Weighted- Average Exercise Price (per share)		Weighted- Average Remaining Contract Life (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2017	3,659,791		$	6.88	4.38	$	59,436
Granted	17,988		22.81
Exercised	(5,000	)	6.74			$	111
Forfeited or cancelled	(13,780	)	12.19
Outstanding as of March 31, 2018	3,658,999		$	6.94	4.14	$	94,116

Options vested and exercisable at March 31, 2018	3,227,445		$	6.30	3.60	$	85,078

Options vested and expected to vest as of March 31, 2018	3,647,576		$	6.92	4.13	$	93,891

Summary of Restricted Stock Unit Activity

The following summarizes the restricted stock unit activity for the periods presented:



	Number of Awards Outstanding		Weighted-Average Grant Date Fair Value (per share)		Aggregate Intrinsic Value (in thousands)
Nonvested RSUs as of December 31, 2017	—		$	—	$	—
Granted	316,643		25.69
Vested	(4,046	)	22.81
Forfeited or cancelled	(320	)	28.58
Nonvested RSUs as of March 31, 2018	312,277		$	25.72	$	2,167

Schedule of Stock-Based Compensation Expense in Continuing Operations

The Company recognized total stock-based compensation expense in continuing operations as follows:



	Three Months Ended March 31,
	2017		2018
Cost of revenue	$	20	$	18
Research and development	31		74
Sales and marketing	27		78
General and administrative	168		323
Total	$	246	$	493

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments for Operating Leases

Future minimum lease payments required under operating leases as of March 31, 2018 are as follows:



	Amount
2018 (remaining)	$	3,145
2019	5,004
2020	5,180
2021	5,254
2022	3,438
Thereafter	3,742
	$	25,763

Schedule of Future Minimum Lease Receipts for Operating Lease

Future minimum sub-lease receipts required under the non-cancellable lease as of March 31, 2018 are as follows:



	Amount
2018 (remaining)	$	769
2019	1,042
2020	1,065
2021	1,089
2022	594
Thereafter	$	4,559

Basic and Diluted Income per Common Share (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The components of basic and diluted earnings per share, or EPS, are as follows:



	Three Months Ended March 31,
	2017		2018
Earnings per share
Net income	$	2,989	$	6,191
Less: net income allocated to participating securities	391		—
Net income attributable to common stockholders	$	2,598	$	6,191
Net income per share:
Basic	$	0.22	$	0.35
Diluted	$	0.20	$	0.30
Weighted Average Number of Common Shares Outstanding
Basic	11,798,565		17,658,611
Dilutive effect of stock options, restricted stock units, and warrants	1,174,044		2,826,142
Diluted	12,972,609		20,484,753

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following common share equivalents have been excluded from the calculation of weighted-average common shares outstanding, because the effect is anti-dilutive for the periods presented:



	Three Months Ended March 31,
	2017	2018
Anti-dilutive Disclosure
Series A redeemable convertible preferred stock outstanding	1,775,000	—
Stock options issued and outstanding	588,365	94,126

Organization and Description of Business (Details)	3 Months Ended
Organization and Description of Business (Details)	Mar. 31, 2018 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	2
Number of reportable segments	2

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 38,773	$ 37,627
Restricted cash	200	243
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 38,973	$ 37,870	$ 5,740	$ 7,028

Summary of Significant Accounting Policies (Details)	12 Months Ended
Summary of Significant Accounting Policies (Details)	Dec. 31, 2017
Customer One \| Accounts Receivable
Concentration Risk [Line Items]
Concentration risk percentage	13.00%

Fair Value of Financial Instruments - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, amortized cost or carrying value	$ 38,773	$ 37,627
Cash and cash equivalents, net unrealized losses	0
Marketable securities, amortized cost or carrying value	8,500
Marketable securities, net unrealized losses	(8)
Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, net unrealized losses	0
U.S. Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, net unrealized losses	0
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, amortized cost or carrying value	8,500
Marketable securities, net unrealized losses	(8)
Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value	38,041
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, amortized cost or carrying value	29,541
Cash and cash equivalents, fair value	29,541	28,015
Marketable securities, fair value	8,492
Total financial assets, fair value	38,033
Fair Value, Measurements, Recurring \| Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, amortized cost or carrying value	15,541
Cash and cash equivalents, fair value	15,541
Fair Value, Measurements, Recurring \| U.S. Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, amortized cost or carrying value	14,000
Cash and cash equivalents, fair value	14,000
Fair Value, Measurements, Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	8,492
Fair Value, Measurements, Recurring \| Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		28,015
Level 1 \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	15,541	28,015
Marketable securities, fair value	0
Total financial assets, fair value	15,541
Level 1 \| Fair Value, Measurements, Recurring \| Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	15,541
Level 1 \| Fair Value, Measurements, Recurring \| U.S. Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0
Level 1 \| Fair Value, Measurements, Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	0
Level 1 \| Fair Value, Measurements, Recurring \| Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		28,015
Level 2 \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	14,000	0
Marketable securities, fair value	8,492
Total financial assets, fair value	22,492
Level 2 \| Fair Value, Measurements, Recurring \| Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0
Level 2 \| Fair Value, Measurements, Recurring \| U.S. Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	14,000
Level 2 \| Fair Value, Measurements, Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	8,492
Level 2 \| Fair Value, Measurements, Recurring \| Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		0
Level 3 \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0	0
Marketable securities, fair value	0
Total financial assets, fair value	0
Level 3 \| Fair Value, Measurements, Recurring \| Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0
Level 3 \| Fair Value, Measurements, Recurring \| U.S. Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0
Level 3 \| Fair Value, Measurements, Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	$ 0
Level 3 \| Fair Value, Measurements, Recurring \| Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		$ 0

Fair Value of Financial Instruments - Contractual Maturities of Marketable Securities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 8,500
Aggregate Fair Value	8,492
Interest earned on marketable securities	16
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	8,500
Aggregate Fair Value	$ 8,492

Financial Statement Components - Accounts Receivable, Net of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial Statement Components [Abstract]
Trade accounts receivable	$ 15,002	$ 44,692
Unbilled accounts receivable	10,335	8,653
Allowance for doubtful accounts	(1,290)	(32,463)
Other accounts receivable	357	343
Total accounts receivable, net	$ 24,404	$ 21,225

Financial Statement Components - Allowance For Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allowance for Doubtful Accounts Receivable [Roll Forward]
Revenue	$ 53,012	$ 39,625
Carrier Access Billing (CAB)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Billings deemed not probable of collection	118	2,463
Revenue recognized as a result of settlement agreement	(6,268)
Billed	4,079	4,611
Revenue	3,961	2,148
Accounts Receivable, Excluding Carrier Access Billing (CAB)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period	189	255
Billings deemed not probable of collection	1	(43)
Deductions	(48)	(124)
Balance, end of period	142	88
Carrier Access Billing (CAB)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period	32,274	22,316
Write-off of previously outstanding and fully reserved billings related to settlement	(24,968)	0
Billings deemed not probable of collection	118	2,463
Revenue recognized as a result of settlement agreement	(6,268)	0
Deductions	(8)	(43)
Balance, end of period	$ 1,148	$ 24,736

Financial Statement Components (Details) - USD ($)		3 Months Ended
Financial Statement Components (Details) - USD ($)	Feb. 08, 2018	Mar. 31, 2018	Mar. 31, 2017
Carrier Access Billing (CAB)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Settlement agreement lump sum payment	$ 4,400,000
Revenue recognized as a result of settlement agreement		$ 6,268,000
Carrier Access Billing (CAB)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Write-off of previously outstanding and fully reserved billings related to settlement		24,968,000	$ 0
Revenue recognized as a result of settlement agreement		$ 6,268,000	$ 0

Financial Statement Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial Statement Components [Abstract]
Accrued expense	$ 7,878	$ 6,851
Accrued compensation and benefits	2,809	5,237
Accrued sales, use, and telecom related taxes	3,146	3,030
Other accrued expenses	638	515
Total accrued expenses	$ 14,471	$ 15,633

Property and Equipment - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 46,348	$ 44,373
Less—accumulated depreciation	(30,446)	(29,427)
Total property and equipment, net	15,902	14,946
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	872	863
Computer and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,450	7,545
Telecommunications equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	21,490	19,985
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	453	453
Software development costs
Property, Plant and Equipment [Line Items]
Property and equipment, gross	16,073	15,517
Automobile
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 10	$ 10

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Capitalized software development costs	$ 441	$ 677
Amortization of capitalized software development costs	$ 448	$ 580

Property and Equipment - Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Depreciation Expense [Line Items]
Depreciation	$ 1,222	$ 1,166
Cost of revenue
Depreciation Expense [Line Items]
Depreciation	1,064	1,047
Research and development
Depreciation Expense [Line Items]
Depreciation	29	10
Sales and marketing
Depreciation Expense [Line Items]
Depreciation	10	7
General and administrative
Depreciation Expense [Line Items]
Depreciation	$ 119	$ 102

Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ (7,615)		$ (7,450)
Finite-lived intangible assets, net	6,714
Gross Amount	15,093		15,093
Net Carrying Value	7,478		7,643
Licenses
Indefinite-lived Intangible Assets [Line Items]
Licenses, indefinite lived	764		764
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	10,396		10,396
Accumulated Amortization	(3,682)		(3,552)
Finite-lived intangible assets, net	$ 6,714		6,844
Amortization Period	20 years	20 years
Domain name and related trademarks
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 2,678		2,678
Accumulated Amortization	(2,678)		(2,643)
Finite-lived intangible assets, net	$ 0		35
Domain name and related trademarks \| Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization Period	3 years	3 years
Domain name and related trademarks \| Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization Period	7 years	7 years
Licenses
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 341		341
Accumulated Amortization	(341)		(341)
Finite-lived intangible assets, net	$ 0		0
Amortization Period	2 years	2 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 139		139
Accumulated Amortization	(139)		(139)
Finite-lived intangible assets, net	$ 0		0
Non-compete agreements \| Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization Period	2 years	2 years
Non-compete agreements \| Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization Period	5 years	5 years
Developed technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 775		775
Accumulated Amortization	(775)		(775)
Finite-lived intangible assets, net	$ 0		$ 0
Amortization Period	3 years	3 years

Intangible Assets - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 165	$ 210
Weighted average amortization period for all definite lived intangible assets	19 years

Intangible Assets - Future Estimated Amortization Expense (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2018 (remaining)	$ 390
2019	520
2020	520
2021	520
2022	520
Thereafter	4,244
Finite-lived intangible assets, net	$ 6,714

Debt - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Cost of assets under capital leases	$ 1,951	$ 1,951
Accumulated depreciation of assets under capital leases	1,863	1,821
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit	0
Available borrowing capacity	25,000
Outstanding unamortized loan fees	$ 159	$ 175

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Debt - Remaining Payments due on Capital Lease Obligations (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Debt Disclosure [Abstract]
2018 (remaining)	$ 67
Less amount representing interest	0
Capital lease obligations	67
Less current maturities	67
Capital lease obligations, noncurrent	$ 0

Segment and Geographic Information - Reconciliation of Segment Profit (Loss) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment	2
Revenue	$ 53,012	$ 39,625
Cost of revenue	25,364	21,566
Gross profit	27,648	18,059
CPaaS
Segment Reporting Information [Line Items]
Revenue	38,897	31,647
Cost of revenue	21,905	18,228
Gross profit	16,992	13,419
Other
Segment Reporting Information [Line Items]
Revenue	14,115	7,978
Cost of revenue	3,459	3,338
Gross profit	$ 10,656	$ 4,640

Segment and Geographic Information - Reconciliation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 53,012	$ 39,625
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	52,824	39,518
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 188	$ 107

Stockholders' Equity (Details)	Mar. 31, 2018 vote $ / shares shares	Dec. 31, 2017 vote $ / shares shares
Class of Stock [Line Items]
Preferred A stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred A stock, par value (in usd per share) \| $ / shares		$ 0.001
Preferred A stock, shares issued (in shares)	0	0
Preferred A stock, shares outstanding (in shares)	0	0
Common Class A
Class of Stock [Line Items]
Preferred A stock, par value (in usd per share) \| $ / shares	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock voting rights, votes per share (in vote) \| vote	1	1
Common stock, par value (in usd per share) \| $ / shares	$ 0.001	$ 0.001
Common stock, shares issued (in shares)	4,202,831	4,197,831
Common stock, shares outstanding (in shares)	4,202,831	4,197,831
Common Class B
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock voting rights, votes per share (in vote) \| vote	10	10
Common stock, par value (in usd per share) \| $ / shares	$ 0.001	$ 0.001
Common stock, shares issued (in shares)	13,489,628	13,440,724
Common stock, shares outstanding (in shares)	13,489,628	13,440,724

Stockholders' Equity - Reserved Shares of Common Stock for Issuance (Details) - shares	Mar. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	4,891,011	4,761,141
Stock options issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	3,658,999	3,659,791
Nonvested restricted stock units issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	312,277	0
Stock purchase warrants issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	0	51,350
Stock-based awards available for grant under the 2017 Plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	919,735	1,050,000

Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Jan. 01, 2018	Nov. 09, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)			4,891,011		4,761,141
Estimated grant date fair value of options vested			$ 111	$ 117
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized cost for stock based compensation			$ 1,869
Unrecognized cost for stock based compensation, period for recognition (in years)			2 years 6 months 18 days
Nonvested restricted stock units issued and outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)			312,277		0
Vesting percentage			25.00%
Unrecognized cost for stock based compensation, period for recognition (in years)			3 years 10 months 6 days
Unrecognized compensation cost related to non-vested RSUs			$ 7,874
2017 Equity Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)		1,050,000
Common stock reserved for future issuance, percent increase	5.00%
Increase in shares available for grant (in shares)	200,000
2010 Equity Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options granted (in usd per share)			$ 11.10	$ 4.34
2010 Equity Compensation Plan \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)		4 years
Contractual life (in years)		10 years

Stock Based Compensation - Fair Value of Options Granted Using the Black-Scholes Pricing Model (Details) - Employee Stock Option - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Expected stock price volatility	47.00%	44.00%
Average risk-free interest rate	2.50%
Average risk-free interest rate, minimum		2.00%
Average risk-free interest rate, maximum		2.30%
Expected life (in years)	6 years 2 months 12 days	6 years 2 months 12 days
Fair value of common stock (in usd per share)	$ 22.81	$ 9.60

Stock Based Compensation - Stock Option Activity (Details) - Employee Stock Option - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options outstanding, beginning balance (in shares)	3,659,791
Number of options, granted (in shares)	17,988
Number of options exercised (in shares)	(5,000)
Number of options, forfeited or cancelled (in shares)	(13,780)
Number of options outstanding, ending balance (in shares)	3,658,999
Number of options outstanding, options vested and exercisable (in shares)	3,227,445
Number of options outstanding, options vested and expected to vest (in shares)	3,647,576
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, beginning balance (in usd per share)	$ 6.88
Weighted-average exercise price, granted (in usd per share)	22.81
Weighted-average exercise price, exercised (in usd per share)	6.74
Weighted-average exercise price, forfeited or cancelled (in usd per share)	12.19
Weighted-average exercise price, ending balance (in usd per share)	6.94
Weighted-average exercise price, options vested and exercisable (in usd per share)	6.30
Weighted-average exercise price, options vested and expected to vest (in usd per share)	$ 6.92
Weighted-average remaining contract life, options outstanding (in years)	4 years 1 month 21 days	4 years 4 months 17 days
Weighted-average remaining contract life, options vested and exercisable (in years)	3 years 7 months 6 days
Weighted-average remaining contract life, options vested and expected to vest (in years)	4 years 1 month 17 days
Aggregate intrinsic value, options outstanding	$ 94,116		$ 59,436
Aggregate intrinsic value, options exercised	111
Aggregate intrinsic value, options vested and exercisable	85,078
Aggregate intrinsic value, options vested and expected to vest	$ 93,891

Stock Based Compensation - Restricted Stock Unit Activity (Details) - Nonvested restricted stock units issued and outstanding - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Number of nonvested RSUs outstanding, beginning balance (in shares)	0
Number of nonvested RSUs, granted (in shares)	316,643
Number of nonvested RSUs, vested (in shares)	(4,046)
Number of nonvested RSUs, forfeited or cancelled (in shares)	(320)
Number of nonvested RSUs outstanding, ending balance (in shares)	312,277
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, beginning balance (in usd per share)	$ 0.00
Weighted average grant-date fair value of nonvested RSUS, granted (in usd per share)	25.69
Weighted-average grant date fair value of nonvested RSUs, vested (in usd per share)	22.81
Weighted-average grant date fair value of nonvested restricted RSUs, forfeited or cancelled (in usd per share)	28.58
Weighted-average grant date fair value, ending balance (in usd per share)	$ 25.72
Aggregate intrinsic value, nonvested RSUs outstanding	$ 2,167	$ 0

Stock Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 493	$ 246
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	18	20
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	74	31
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	78	27
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 323	$ 168

Commitments and Contingencies (Details)				3 Months Ended
Commitments and Contingencies (Details)	Mar. 27, 2018 ft²	Feb. 08, 2018 USD ($)	Jan. 12, 2018 ft²	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Apr. 14, 2017 ft²
Lessee, Lease, Description [Line Items]
Term of lease (in months)	60 months		84 months
Office space (in square foot) \| ft²	5,930		40,035			40,657
Rent expense				$ 933,000	$ 513,000
Annual minimum commitments				$ 1,200,000
Term of agreement (in years)				5 years
Non-cancellable purchase obligation				$ 6,112,000
General and administrative
Lessee, Lease, Description [Line Items]
Reduction of rent expense				$ (251,000)	$ (230,000)
Carrier Access Billing (CAB)
Lessee, Lease, Description [Line Items]
Settlement agreement lump sum payment		$ 4,400,000

Commitments and Contingencies - Future Minimum Rental Payments for Operating Leases (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2018 (remaining)	$ 3,145
2019	5,004
2020	5,180
2021	5,254
2022	3,438
Thereafter	3,742
Future minimum payments due, total	$ 25,763

Commitments and Contingencies - Future Minimum Lease Receipts (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2018	$ 769
2019	1,042
2020	1,065
2021	1,089
2022	594
Future minimum lease receipts, total	$ 4,559

Employee Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended
Employee Benefit Plan (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Retirement Benefits [Abstract]
Matching contributions	$ 287	$ 351

Income Taxes - Additional Information (Details)	3 Months Ended
Income Taxes - Additional Information (Details)	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Effective tax rate	29.80%	37.20%

Related Parties (Details) - Affiliated Entity - Republic - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Transition Services Agreement
Related Party Transaction [Line Items]
Revenue from related parties	$ 28,000	$ 351,000
Due from related parties	11,000		$ 15,000
Facilities Sharing Agreement
Related Party Transaction [Line Items]
Rental payments received	251,000	230,000
Due from related parties	0		0
Tax Sharing Agreement
Related Party Transaction [Line Items]
Due from related parties			0
Due to related parties			0
Master Services Agreement
Related Party Transaction [Line Items]
Revenue from related parties	986,000	$ 534,000
Due from related parties	$ 310,000		$ 311,000

Basic and Diluted Income per Common Share - Components of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 6,191	$ 2,989
Less: net income allocated to participating securities	0	391
Net income attributable to common stockholders	$ 6,191	$ 2,598
Net income per share:
Basic (in usd per share)	$ 0.35	$ 0.22
Diluted (in usd per share)	$ 0.30	$ 0.20
Weighted Average Number of Common Shares Outstanding
Basic (in shares)	17,658,611	11,798,565
Dilutive effect of stock options, restricted stock units, and warrants (in shares)	2,826,142	1,174,044
Diluted (in shares)	20,484,753	12,972,609

Basic and Diluted Income per Common Share - Antidilutive Securities Excluded from the Computation (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Series A redeemable convertible preferred stock outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from calculation of weighted-average common shares outstanding	0	1,775,000
Stock options issued and outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from calculation of weighted-average common shares outstanding	94,126	588,365