Bandwidth (BAND) 10-Q 3 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 2019
Class of Stock [Line Items]
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Entity Registrant Name	Bandwidth Inc.
Trading Symbol	BAND
Entity Central Index Key	0001514416
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	false
Common Class A
Class of Stock [Line Items]
Entity Common Stock, Shares Outstanding		16,546,956
Common Class B
Class of Stock [Line Items]
Entity Common Stock, Shares Outstanding		6,453,501

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 138,871	$ 41,261
Marketable securities	59,520	17,400
Accounts receivable, net of allowance for doubtful accounts	27,898	24,009
Prepaid expenses and other current assets	6,971	6,114
Deferred costs	2,344	2,630
Total current assets	235,604	91,414
Property and equipment, net	26,363	25,136
Intangible assets, net	6,959	7,089
Deferred costs, non-current	1,433	1,828
Other long-term assets	1,409	727
Goodwill	6,867	6,867
Deferred tax asset	25,020	17,359
Total assets	303,655	150,420
Current liabilities:
Accounts payable	3,369	3,418
Accrued expenses and other current liabilities	21,768	21,393
Current portion of deferred revenue	5,421	5,324
Advanced billings	2,203	2,588
Total current liabilities	32,761	32,723
Deferred rent, net of current portion	2,660	2,503
Deferred revenue, net of current portion	6,359	6,424
Total liabilities	41,780	41,650
Stockholders’ equity:
Class A and Class B common stock	23		$ 19
Additional paid-in capital	267,875	116,600
Accumulated deficit	(6,030)	(7,848)
Accumulated other comprehensive (loss) income	7	(1)
Total stockholders’ equity	261,875	108,770	$ 76,711
Total liabilities and stockholders’ equity	$ 303,655	$ 150,420

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 53,321	$ 53,012
Cost of revenue	28,766	25,364
Gross profit	24,555	27,648
Operating expenses:
Research and development	7,717	3,781
Sales and marketing	8,349	4,522
General and administrative	14,333	10,569
Total operating expenses	30,399	18,872
Operating income (loss)	(5,844)	8,776
Other income, net	201	49
Income (loss) before income taxes	(5,643)	8,825
Income tax (provision) benefit	7,635	(2,634)
Net income	1,992	6,191
Other Comprehensive income
Unrealized (loss) gain on marketable securities, net of income taxes	8	(6)
Total comprehensive income	2,000	6,185
Net income attributable to common stockholders	$ 1,992	$ 6,191
Net income per share:
Basic (in usd per share)	$ 0.10	$ 0.35
Diluted (in usd per share)	$ 0.09	$ 0.30
Weighted average number of common shares outstanding:
Basic (in shares)	20,498,104	17,658,611
Diluted (in shares)	21,975,944	20,484,753

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Class A voting common Stock	Class B voting common Stock	Common stockClass A voting common Stock	Common stockClass A voting common StockConversion of Class B voting common stock to Class A voting common stock	Common stockClass B voting common Stock	Common stockClass B voting common StockConversion of Class B voting common stock to Class A voting common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit
Common stock, shares outstanding, beginning balance (in shares) at Dec. 31, 2017				4,197,831		13,440,725
Beginning balance at Dec. 31, 2017	$ 76,711			$ 4		$ 13		$ 102,465	$ 0	$ (25,771)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)				5,000
Exercises of vested stock options	35			$ 1				34
Exercise of warrants to purchase common stock (in shares)						48,904
Exercise of warrants to purchase common stock	36							36
Costs in connection with public offering	(285)							(285)
Unrealized (loss) gain on marketable securities	(6)								(6)
Stock based compensation	493							493
Net income	6,191									6,191
Common stock, shares outstanding, ending balance (in shares) at Mar. 31, 2018				4,202,831		13,489,629
Ending balance at Mar. 31, 2018	83,175			$ 5		$ 13		102,743	(6)	(19,580)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)				1,112,646
Exercises of vested stock options	6,933			$ 1				6,932
Vesting of restricted stock units (in shares)				6,512
Issuance of common stock (in shares)				330
Unrealized (loss) gain on marketable securities	4								4
Stock based compensation	762							762
Conversion of stock (in shares)					6,052,910		(6,052,910)
Conversion of stock	0				$ 6		$ (6)
Net income	10,512									10,512
Common stock, shares outstanding, ending balance (in shares) at Jun. 30, 2018				11,375,229		7,436,719
Ending balance at Jun. 30, 2018	101,386			$ 12		$ 7		110,437	(2)	(9,068)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)				534,474
Exercises of vested stock options	3,579							3,579
Vesting of restricted stock units (in shares)				2,466
Unrealized (loss) gain on marketable securities	(1)								(1)
Stock based compensation	762							762
Conversion of stock (in shares)					435,313		(435,313)
Net income	2,510									2,510
Common stock, shares outstanding, ending balance (in shares) at Sep. 30, 2018				12,347,482		7,001,406
Ending balance at Sep. 30, 2018	108,236			$ 12		$ 7		114,778	(3)	(6,558)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)				72,569
Exercises of vested stock options	500							500
Vesting of restricted stock units (in shares)				2,022
Unrealized (loss) gain on marketable securities	2								2
Stock based compensation	1,322							1,322
Conversion of stock (in shares)					490,674		(490,674)
Conversion of stock	0				$ 1		$ (1)
Net income	(1,290)									(1,290)
Common stock, shares outstanding, ending balance (in shares) at Dec. 31, 2018		12,912,747	6,510,732	12,912,747		6,510,732
Ending balance at Dec. 31, 2018	108,770			$ 13		$ 6		116,600	(1)	(7,848)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to opening retained earnings due to adoption of ASC 606	(174)									(174)
Exercises of vested stock options (in shares)				589,510
Exercises of vested stock options	3,935			$ 1				3,934
Vesting of restricted stock units (in shares)				105,367
Issuance of common stock (in shares)				2,875,000
Issuance of common stock	147,391			$ 3				147,388
Costs in connection with public offering	(785)							(785)
Unrealized (loss) gain on marketable securities	8								8
Stock based compensation	1,676							1,676
Conversion of stock (in shares)				57,230		(57,230)
Equity awards withheld for tax liability (in shares)				(16,585)
Equity awards withheld for tax liability	(938)							(938)
Net income	1,992									1,992
Common stock, shares outstanding, ending balance (in shares) at Mar. 31, 2019		16,523,269	6,453,502	16,523,269		6,453,502
Ending balance at Mar. 31, 2019	$ 261,875			$ 17		$ 6		$ 267,875	$ 7	$ (6,030)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities
Net income	$ 1,992	$ 6,191
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	2,209	1,387
Accretion of bond discount	(119)	(6)
Amortization of debt issuance costs	122	16
Stock-based compensation	1,676	493
Deferred taxes	(7,664)	2,611
Loss on disposal of property and equipment	296	9
Changes in operating assets and liabilities:
Accounts receivable	(3,889)	(3,179)
Prepaid expenses and other assets	(1,552)	(471)
Deferred costs	604	146
Accounts payable	(435)	(656)
Accrued expenses and other liabilities	(1,729)	(1,165)
Deferred revenue and advanced billings	(527)	5,876
Deferred rent	(19)	(9)
Net cash provided by (used in) operating activities	(9,035)	11,243
Investing activities
Purchase of property and equipment	(1,239)	(961)
Capitalized software development costs	(595)	(441)
Purchase of marketable securities	(50,990)	(8,498)
Maturities of marketable securities	9,000	0
Net cash used in investing activities	(43,824)	(9,900)
Financing activities
Proceeds from the follow-on public offering, net of underwriting discounts	147,391	0
Payments on capital leases	0	(25)
Payment of debt issuance costs	(125)	0
Proceeds from exercises of stock options	3,935	34
Proceeds from exercises of warrants	0	36
Equity awards withheld and paid for tax liabilities	(589)	0
Net cash (used in) provided by financing activities	150,453	(240)
Net increase in cash, cash equivalents, and restricted cash	97,594	1,103
Cash, cash equivalents, and restricted cash, beginning of period	41,501	37,870
Cash, cash equivalents, and restricted cash, end of period	139,095	38,973
Supplemental disclosure of cash flow information
Cash paid during the period for interest	33	19
Cash paid for taxes	114	90
Supplemental disclosure of noncash investing and financing activities
Purchase of property and equipment, accrued but not paid	1,768	785
Costs related to the follow-on public offering, accrued but not paid	549	0
Equity awards withheld for tax liabilities, accrued but not paid	349	0
Follow-on Public Offering
Financing activities
Payments of costs related to public offering	(159)	0
IPO
Financing activities
Payments of costs related to public offering	$ 0	$ (285)

Organization and Description of

Organization and Description of Business	3 Months Ended
	Mar. 31, 2019
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. Follow-on Public Offering

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
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 15, 2019. The condensed consolidated balance sheet as of December 31, 2018, 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. Additionally, certain items in the prior period financial statements have been reclassified to conform with the current year presentation. 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 2019 or any future period. Reclassification The Company reclassified certain prior year amounts to conform to the current year presentation. These reclassifications had no impact on the previously reported total assets, liabilities, stockholder’s deficit or net income. Principles of Consolidation The condensed 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 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, 2018 2019 Cash and cash equivalents $ 41,261 $ 138,871 Restricted cash 240 224 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 41,501 $ 139,095 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, 2018, one customer represented approximately 18% of the Company’s accounts receivable, net of allowance for doubtful accounts. As of March 31, 2019, one customer represented approximately 16% of the Company’s accounts receivable, net of allowance for doubtful accounts. For the three months ended March 31, 2018 and 2019, no individual customer represented more than 10% of the Company’s total revenue. Recently Adopted Accounting Standards On January 1, 2019, the Company adopted the guidance of ASC 606, Revenue from Contracts with Customers, using the modified retrospective method applied to those contracts which were not completed as of January 1, 2019. The Company ’ s results for reporting periods beginning after January 1, 2019 are presented in accordance with the provisions under ASC 606 and prior period amounts have not been adjusted and continue to be reported in accordance with the Company ’ s revenue recognition policy as further described in Note 2, Summary of Significant Accounting Policies, to its Annual Report on Form 10-K for the year ended December 31, 2018. In connection with the adoption of ASC 606, the Company recognized a net increase to its opening accumulated deficit of $174 as of January 1, 2019, related to a discount present in one of its contracts. Prior to the adoption of ASC 606, the Company recognized the majority of its revenue based on the usage of its customers in the period the traffic traversed the Company ’ s network. The Company determined that ASC 606 continues to support the recognition of revenue over time for the majority of the Company ’ s contracts due to the continuous transfer of control to the customer. The adoption of ASC 606 did not result in a change in the Company ’ s accounting for its commission costs, which will continue to be expensed as incurred. The Company pays commissions over time and a corresponding requisite substantive service condition exists for the employee to receive the commission. The Company determined the timing of the commission payments and the underlying service performed by the employee were commensurate. The impact on the Company ’ s balance sheet presentation includes separately presenting customer refundable prepayments as advanced billings, whereas under ASC 605 these were included in the current portion of deferred revenue and advanced billings. Revenue Recognition Revenue recognition commences upon transfer of control of promised goods or services to customers in an amount that the Company expects to receive in exchange for those products or services. The Company determines revenue recognition through the following steps: • i dentification of the contract, or contracts, with a customer; • i dentification of the performance obligations in the contract; • d etermination of the transaction price; • a llocation of the transaction price to the performance obligations in the contract; and • r ecognition of revenue, when, or as, the Company satisfies a performance obligation. Nature of Products and Services Revenue consists primarily of the sale of communications services offered through Application Programming Interface (“API”) software solutions to large enterprise, as well as small and medium-sized business, customers and is generally derived from usage and service fees in both the CPaaS and Other segments. Usage revenue includes voice communication (primarily driven by inbound minutes, outbound minutes and toll-free minutes) and messaging communication (driven by the number of messages) that traverse the platform and network. Service fees include the provision and management of phone numbers and emergency services access. The majority of the Company ’ s revenue is generated from usage-based fees earned from customers accessing the Company ’ s communications platform. Access to the Company ’ s communication platform is considered a series of distinct services, with continuous transfer of control to the customer, comprising one performance obligation and usage-based fees are recognized in revenue in the period the traffic traverses the Company ’ s network. For the three months ended March 31, 2018, the revenue from usage-based fees represented $24,568 of CPaaS revenue and $12,164 of Other revenue. For the three months ended March 31, 2019, the revenue from usage-based fees represented $29,050 of CPaaS revenue and $6,792 of Other revenue. Revenue from service fees is recognized on a ratable basis as the service is provided, which is typically one month. For the three months ended March 31, 2018, the revenue from service fees represented $13,685 of CPaaS revenue and $1,951 of Other revenue. For the three months ended March 31, 2019, the revenue from service fees represented $14,754 of CPaaS revenue and $1,516 of Other revenue. The remaining $644 and $1,209 for the three months ended March 31, 2018 and 2019, respectively, are generated from other miscellaneous services. Infrequently, Bandwidth ’ s contracts with customers may include multiple performance obligations. For such arrangements, revenues are allocated to each performance obligation based on its relative standalone selling price. Generally, standalone selling prices are determined based on the prices charged to similar customers for similar services. When required as part of providing service, revenues and associated expenses related to nonrefundable, upfront service activation and setup fees are deferred and recognized over the longer of the associated service contract period or estimated customer life. The Company ’ s contracts do not contain general rights of return. However, occasionally credits may be issued. The Company ’ s contracts do not provide customers with the right to take possession of the software supporting the applications. Amounts that have been invoiced are recorded in accounts receivable and in revenue or deferred revenue depending on whether the revenue recognition criteria have been met. The Company maintains a reserve for sales credits. Credits are accounted for as variable consideration and are estimated based on several inputs including historical experience and current trends of credit issuances. Adjustments to the reserve are recorded against revenue. The Company has various sales commission plans for which eligible employees can earn commissions from the sale of products and services to customers. Eligible employees must be employed at the time of payment in order to receive a commission. The Company pays commissions over time and a corresponding requisite substantive service condition exists for the employee to receive the commission. The Company determined that the timing of the commission payments and the underlying service performed by the employee were commensurate. Accordingly, sales commissions are generally expensed as incurred. These costs are recorded within sales and marketing expenses. Contract Assets and Liabilities The following table provides information about receivables and contract liabilities from contracts with customers: March 31, 2019 Receivables (1) $ 27,898 Contract liabilities (2) 11,780 ________________________ (1) Included in accounts receivable, net of allowance on the consolidated balance sheet. (2) Included in current portion of deferred revenue and deferred revenue, net of current portion on the consolidated balance sheet. Deferred revenue is recorded when cash payments are received in advance of future usage on contracts. Customer refundable payments are recorded as advanced billings. Revenue is typically recognized in the month following when service is rendered or, in the case of nonrefundable upfront fees, over the estimated period of benefit. During the three months ended March 31, 2019, the Company recognized revenue of $2,218, related to its contract liabilities. The Company expects to recognize $5,421 in revenue over the next twelve months related to its deferred revenue as of March 31, 2019. Other than adoption of ASC 606, there were no changes to the Company ’ s significant accounting policies as described in its Annual Report on Form 10-K for the year ended December 31, 2018. Recent Accounting Pronouncements Not Yet Adopted In October 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-17, Consolidation (Topic 810), Targeted Improvements to Related Party Guidance for Variable Interest Entities , which addresses the cost and complexity of financial reporting associated with consolidation of variable interest entities (“VIE”). ASU 2018-17 is effective for emerging growth companies following private company adoption dates in fiscal years beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020, with early adoption permitted. The new guidance must be applied on a retrospective basis as a cumulative-effect adjustment as of the date of adoption. Management does not expect the adoption of this guidance to have a significant impact on the Company’s financial statements. In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract . This standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 is effective for emerging growth companies following private company adoption dates in fiscal years beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates certain disclosure requirements for fair value measurements for all entities, requires public entities to disclose certain new information and modifies some disclosure requirements. ASU 2018-13 is effective for all entities for fiscal years beginning after December 15, 2019 and for interim periods within those fiscal years, and early adoption is permitted. An entity is permitted to early adopt either the entire standard or only the provisions that eliminate or modify requirements. 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 public business entities that are U.S. SEC filers 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 statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments–Credit Losses: Measurement of Credit Losses on Financial Instruments , which changes the impairment model for most financial assets. The new model uses a forward-looking expected loss method, which will generally result in earlier recognition of allowances for losses. In November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments – Credit Losses , which clarifies that receivables arising from operating leases are not within the scope of Topic 326, Financial Instruments – Credit Losses. Instead, impairment of receivables arising from operating leases should be accounted for in accordance with Topic 842, Leases. These ASUs are effective for public business entities that are SEC filers for annual and interim periods beginning after December 15, 2019 and early adoption is permitted for annual and interim periods beginning after December 15, 2018. The Company is evaluating the impact of this guidance on its consolidated financial statements. 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. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, Leases, to clarify how to apply certain aspects of the new leases standard. In July 2018, the FASB also issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, to give entities another option for transition and to provide lessors with a practical expedient to reduce the cost and complexity of implementing the new standard. The transition option allows entities to not apply the new leases standard in the comparative periods they present in their financial statements in the year of adoption. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements, to clarify how to apply certain aspects of the new lease standard. ASU 2016-02 is effective for emerging growth companies following private company adoption dates in 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.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2019
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, 2018 and March 31, 2019 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. 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, 2018 and March 31, 2019: Amortized cost or carrying value Unrealized gains Unrealized losses Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 8,194 $ — $ — $ 8,194 $ — $ — $ 8,194 U.S. Reverse repurchase agreements 26,000 — — — 26,000 — 26,000 Total included in cash and cash equivalents 34,194 — — 8,194 26,000 — 34,194 Marketable securities: U.S. treasury securities 17,402 — (2) 17,400 — — 17,400 Total marketable securities 17,402 — (2) 17,400 — — 17,400 Total financial assets $ 51,596 $ — $ (2) $ 25,594 $ 26,000 $ — $ 51,594 Amortized cost or carrying value Unrealized gains Unrealized losses Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 17,380 $ — $ — $ 17,380 $ — $ — $ 17,380 U.S. Reverse repurchase agreements 115,000 — — — 115,000 — 115,000 Total included in cash and cash equivalents 132,380 — — 17,380 115,000 — 132,380 Marketable securities: U.S. treasury securities 59,509 11 — 59,520 — — 59,520 Total marketable securities 59,509 11 — 59,520 — — 59,520 Total financial assets $ 191,889 $ 11 $ — $ 76,900 $ 115,000 $ — $ 191,900 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, 2019: Amortized cost Aggregate fair value Financial assets: Less than one year $ 59,509 $ 59,520 Total $ 59,509 $ 59,520 As of March 31, 2019, there were no securities in an unrealized loss position. During the three months ended March 31, 2018 and 2019, there were $0 and $9,000, respectively, in maturities of marketable securities. Interest earned on marketable securities in the three months ended March 31, 2018 and 2019 was $16 and $3, respectively, and is recorded as other income, net, in the accompanying condensed consolidated statements of operations and comprehensive income.

Financial Statement Components

Financial Statement Components	3 Months Ended
	Mar. 31, 2019
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, 2018 2019 Trade accounts receivable $ 13,620 $ 15,559 Unbilled accounts receivable 11,174 13,231 Allowance for doubtful accounts (906) (1,018) Other accounts receivable 121 126 Total accounts receivable, net $ 24,009 $ 27,898 Components of allowance for doubtful accounts are as follows: Three months ended March 31, Allowance for doubtful accounts: 2018 2019 Balance, beginning of period $ (32,463) $ (906) Charged to bad debt expense (1) (132) Deductions (1) 56 20 Billings deemed not probable of collection (2) (118) — Write-off of previously outstanding and fully reserved billings related to settlement (3) 24,968 — Revenue recognized from outstanding billings previously deemed uncollectible related to settlement (3) 6,268 — Balance, end of period $ (1,290) $ (1,018) ________________________ (1) Write off of uncollectible accounts after all collection efforts have been exhausted. (2) Represents amounts billed in the period but where collectability is not probable based on customers collection experience. Amounts were charged to a contra-revenue account. (3) 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. Immediately following receipt of the $4,400 payment, the Company issued to Verizon bill credits with respect to other CABS amounts previously billed and reserved to Verizon of $24,968. The amount credited to Verizon comprised the majority of the allowance for CABS revenue as of December 31, 2017. 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 and the other current outstanding Verizon CABS receivables which had been previously reserved as uncollectible, but for which collection was no longer in doubt as a result of the settlement. The settlement agreement also specifies certain terms for the Company’s CABS billings to Verizon prospectively. Accrued expenses and other current liabilities consisted of the following: December 31, March 31, 2018 2019 Accrued expense $ 8,292 $ 11,440 Accrued compensation and benefits 7,323 4,337 Accrued sales, use, and telecom related taxes 4,742 5,074 Deferred rent, current portion 298 123 Other accrued expenses 738 794 Total accrued expenses and other current liabilities $ 21,393 $ 21,768

Property and Equipment

Property and Equipment	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment, net consisted of the following: December 31, March 31, 2018 2019 Furniture and fixtures $ 1,741 $ 1,793 Computer and office equipment 7,662 7,827 Telecommunications equipment 30,694 31,170 Leasehold improvements 2,438 2,388 Software development costs 16,293 18,728 Automobile 10 10 Total cost 58,838 61,916 Less—accumulated depreciation (33,702) (35,553) Total property and equipment, net $ 25,136 $ 26,363 The Company capitalized $441 and $595 of software development costs in the three months ended March 31, 2018 and 2019, respectively. Amortization expense related to capitalized software development costs were $448 and $789 for the three months ended March 31, 2018 and 2019, respectively. The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows: Three months ended March 31, 2018 2019 Cost of revenue $ 1,064 $ 1,293 Research and development 29 69 Sales and marketing 10 28 General and administrative 119 689 Total depreciation expense $ 1,222 $ 2,079

Intangible Assets

Intangible Assets	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	6. Intangible Assets Intangible assets, net consisted of the following as of December 31, 2018: Gross Accumulated Net Carrying Amortization (Years) Customer relationships $ 10,396 $ (4,071) $ 6,325 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 $ (8,004) $ 7,089 Intangible assets, net consisted of the following as of March 31, 2019: Gross Accumulated Net Carrying Amortization (Years) Customer relationships $ 10,396 $ (4,201) $ 6,195 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 $ (8,134) $ 6,959 Amortization expense for definite lived intangible assets was $165 and $130 for the three months ended March 31, 2018 and 2019, respectively. The remaining amortization period for definite lived intangible assets is 12 years. Future estimated amortization expense for definite lived intangible assets is as follows: As of March 31, 2019 2019 (remaining) $ 390 2020 520 2021 520 2022 520 2023 520 Thereafter 3,725 $ 6,195

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt	7. Debt On March 1, 2019, the Company amended and restated its Credit and Security Agreement with KeyBank National Association. The agreement is for a $25,000 revolving loan, which includes a swing line of up to $1,000 and limits letters of credit commitments to a maximum of $2,500. The term of the amended and restated Credit and Security Agreement is three years and matures on March 1, 2022. Loans under the Credit Agreement will bear interest at the highest of (i) the bank’s prime rate, (ii) the federal funds effective rate plus 0.5 percent, and (iii) the London Interbank Offered Rate plus 1.00 percent. This agreement requires that a specified minimum liquidity amount must be maintained in cash and cash equivalents at all times and that the Company meet a minimum revenue clause on a quarterly basis. As of December 31, 2018 and March 31, 2019, 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, 2019. As of December 31, 2018 and March 31, 2019, the outstanding unamortized loan fees associated with the revolving loan were $136 and $138, respectively, and were included in other long-term assets. On March 1, 2019, previous unamortized loan fees of $125 associated with the Credit and Security agreement prior to the amendment and restatement were expensed to interest expense, which is included in other income, net on the condensed consolidated statements of operations and comprehensive income. Capital Leases The Company leased various equipment under leases accounted for as capital leases with expiration dates through December 2018. As of December 31, 2018, cost and accumulated depreciation of the assets under capital leases recorded by the Company were $1,951 and $1,884, respectively. As of March 31, 2019, cost and accumulated depreciation of the assets under capital leases recorded by the Company were $1,951 and $1,889, respectively. There were no remaining payments due on the Company’s capital lease obligations as of March 31, 2019.

Segment and Geographic Informat

Segment and Geographic Information	3 Months Ended
	Mar. 31, 2019
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 Chief Operating Decision Maker 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, 2018 2019 CPaaS Revenue $ 38,897 $ 45,013 Cost of revenue 21,905 25,300 Gross profit $ 16,992 $ 19,713 Other Revenue $ 14,115 $ 8,308 Cost of revenue 3,459 3,466 Gross profit $ 10,656 $ 4,842 Consolidated Revenue $ 53,012 $ 53,321 Cost of revenue 25,364 28,766 Gross profit $ 27,648 $ 24,555 All assets were held in the United States as of December 31, 2018 and March 31, 2019. The Company generates its revenue primarily in the United States. Revenue by geographic area is detailed in the table below (which is determined based on the customer billing address): Three months ended March 31, 2018 2019 CPaaS United States $ 38,779 $ 44,944 International 118 69 Total $ 38,897 $ 45,013 Other United States $ 14,045 $ 8,229 International 70 79 Total $ 14,115 $ 8,308

Stockholder's Equity

Stockholder's Equity	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity Preferred Stock As of December 31, 2018 and March 31, 2019, 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, 2018 and March 31, 2019, 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, 2018, 12,912,747 and 6,510,732 shares of Class A and B common stock, respectively, were issued and outstanding. As of March 31, 2019, 16,523,269 and 6,453,502 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 Class A common stock for issuance as follows: December 31, March 31, 2018 2019 Stock options issued and outstanding 1,937,370 1,346,119 Nonvested restricted stock units issued and outstanding 324,252 432,240 Stock-based awards available for grant under the 2017 Plan 896,760 1,329,042 3,158,382 3,107,401

Stock Based Compensation

Stock Based Compensation	3 Months Ended
	Mar. 31, 2019
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. On November 9, 2017, the 2010 Plan was terminated in connection with the Company’s initial public offering. 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, 2019, the shares available for grant under the 2017 Plan were automatically increased by 645,637 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. Restricted stock units (“RSU”) 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. Certain RSUs awarded to executives vest over four years with 50% vesting in the first year in 12.5% increments on each calendar quarter immediately following the grant date and the remaining 50% earned over years two, three and four. Other RSUs awarded to executives and employees generally are earned over a service period of four years. Stock options The following summarizes the stock option activity for the periods presented: Number of Weighted- Weighted- Aggregate Outstanding as of December 31, 2018 1,937,370 $ 7.41 4 $ 64,596 Granted — — Exercised (589,510) 6.68 23,804 Forfeited or cancelled (1,741) 11.91 Outstanding as of March 31, 2019 1,346,119 $ 7.72 3.89 $ 79,740 Options vested and exercisable at March 31, 2019 1,107,396 $ 6.69 3.11 $ 66,741 Options vested and expected to vest as of March 31, 2019 1,341,197 $ 7.70 3.87 $ 79,477 Aggregate intrinsic value is computed based on the difference between the option exercise price and the estimated fair value of the Company’s common stock as of March 31, 2019. Prior to the initial public offering, the fair value of the Company’s common stock was estimated by the Company’s board of directors. After the initial public offering, 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. No options were granted for the three months ended March 31, 2019. The weighted average grant-date fair value of stock options granted was $11.10 for the three months ended March 31, 2018. The total estimated grant date fair value of options vested was $111 and $57 for the three months ended March 31, 2018 and 2019, respectively. As of March 31, 2019, total unrecognized compensation cost related to all non-vested stock options was $1,012, which will be amortized over a weighted-average period of 1.87 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) Nonvested RSUs as of December 31, 2018 324,252 $ 26.95 Granted 214,915 41.42 Vested (105,367) 28.07 Forfeited or cancelled (1,560) 35.06 Nonvested RSUs as of March 31, 2019 432,240 $ 33.84 As of March 31, 2019, total unrecognized compensation cost related to non-vested RSUs was $14,118, which will be amortized over a weighted-average period of 3.37 years. Stock-Based Compensation Expense The Company recognized total stock-based compensation expense in continuing operations as follows: Three months ended March 31, 2018 2019 Cost of revenue $ 18 $ 56 Research and development 74 372 Sales and marketing 78 320 General and administrative 323 928 Total $ 493 $ 1,676

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
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 1, 2019, the Company entered into an amendment to an office building lease relating to 117,719 square feet of office space, which includes the Company’s headquarters. The amendment provides an additional 30,114 square feet and extends the lease term to January 31, 2024. In addition, this amendment gives the Company the option to extend the lease for an additional five Future minimum lease payments required under operating leases are as follows: As of March 31, 2019 2019 (remaining) $ 4,402 2020 6,342 2021 6,497 2022 6,210 2023 5,833 Thereafter 2,848 $ 32,132 The Company incurred rent expense of $933 and $1,218 for the three months ended March 31, 2018 and 2019, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations and comprehensive income. On January 1, 2019, the Company entered into an amendment to an office building lease relating to 40,657 square feet of office space, which the Company sub-leases to a related party, Republic Wireless, Inc. (“Republic”). The amendment gives the Company the options to extend the lease for an additional period of approximately 18 months and a subsequent additional five Future minimum sub-lease receipts required under the non-cancellable lease are as follows: As of March 31, 2019 2019 (remaining) $ 785 2020 1,065 2021 1,089 2022 594 $ 3,533 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, as of March 31, 2019 the Company has $6,353 in other non-cancellable purchase obligations, consisting of primarily network equipment maintenance and software license contracts, of which $5,448 will be fulfilled within a 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.

Employee Benefit Plan

Employee Benefit Plan	3 Months Ended
	Mar. 31, 2019
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 $287 and $513 for the three months ended March 31, 2018 and 2019, respectively.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
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 29.8% and 135.2% for the three months ended March 31, 2018 and 2019, respectively. The change in tax rate is primarily due to the impact of stock compensation deductions for tax. 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 this period is higher than the U.S. federal statutory rate of 21% primarily due to the impact of stock compensation tax deductions.

Related Parties

Related Parties	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Parties	14. Related Parties On April 20, 2015, the Company created a wholly owned subsidiary, 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 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, 2018 and 2019, the Company received compensation of $28 and $0, 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 Transition Services Agreement as of December 31, 2018 and March 31, 2019. For the three months ended March 31, 2018 and 2019, the Company received rental payments under the Facilities Sharing Agreement of $251, 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, 2018 and March 31, 2019. 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, 2018 and March 31, 2019. 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, 2018 and 2019, the Company provided telecommunication services to Republic of $986 and $892, respectively. The Company recognized such amounts as revenue in the accompanying condensed consolidated statements of operations and comprehensive income. As of December 31, 2018 and March 31, 2019, the Company had a receivable of $310 and $284, respectively, under the Master Services Agreement. On March 1, 2019 an amendment to the current Master Services Agreement was executed. Pursuant to the terms of the new agreement, Republic receives reduced pricing on its messaging services, effective April 1, 2019. All other terms and conditions of the existing agreement remain. Subsequent to the expiration of the 180-day blackout window on May 9, 2018, Republic employees that held Bandwidth stock options began exercising their options. Upon exercise, Bandwidth withholds the employee tax amounts due from the proceeds. For the three months ended March 31, 2019, Bandwidth had collected on behalf of, and remitted withholding tax to, Republic of $613, and had a related payable of $0 as of March 31, 2019.

Basic and Diluted Income per Co

Basic and Diluted Income per Common Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Basic and Diluted Income per Common Share	15. Basic and Diluted Income per Common Share 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, 2018 2019 Earnings per share Net income attributable to common stockholders $ 6,191 $ 1,992 Net income per share: Basic $ 0.35 $ 0.10 Diluted $ 0.30 $ 0.09 Weighted Average Number of Common Shares Outstanding Basic 17,658,611 20,498,104 Dilutive effect of stock options, restricted stock units, and warrants 2,826,142 1,477,840 Diluted 20,484,753 21,975,944

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	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 15, 2019. The condensed consolidated balance sheet as of December 31, 2018, 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. Additionally, certain items in the prior period financial statements have been reclassified to conform with the current year presentation. 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 2019 or any future period.
Reclassification	Reclassification The Company reclassified certain prior year amounts to conform to the current year presentation. These reclassifications had no impact on the previously reported total assets, liabilities, stockholder’s deficit or net income.
Principles of Consolidation	Principles of Consolidation The condensed 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	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with 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	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	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	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.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards On January 1, 2019, the Company adopted the guidance of ASC 606, Revenue from Contracts with Customers, using the modified retrospective method applied to those contracts which were not completed as of January 1, 2019. The Company ’ s results for reporting periods beginning after January 1, 2019 are presented in accordance with the provisions under ASC 606 and prior period amounts have not been adjusted and continue to be reported in accordance with the Company ’ s revenue recognition policy as further described in Note 2, Summary of Significant Accounting Policies, to its Annual Report on Form 10-K for the year ended December 31, 2018. In connection with the adoption of ASC 606, the Company recognized a net increase to its opening accumulated deficit of $174 as of January 1, 2019, related to a discount present in one of its contracts. Prior to the adoption of ASC 606, the Company recognized the majority of its revenue based on the usage of its customers in the period the traffic traversed the Company ’ s network. The Company determined that ASC 606 continues to support the recognition of revenue over time for the majority of the Company ’ s contracts due to the continuous transfer of control to the customer. The adoption of ASC 606 did not result in a change in the Company ’ s accounting for its commission costs, which will continue to be expensed as incurred. The Company pays commissions over time and a corresponding requisite substantive service condition exists for the employee to receive the commission. The Company determined the timing of the commission payments and the underlying service performed by the employee were commensurate. The impact on the Company ’ s balance sheet presentation includes separately presenting customer refundable prepayments as advanced billings, whereas under ASC 605 these were included in the current portion of deferred revenue and advanced billings.
Revenue Recognition	Revenue Recognition Revenue recognition commences upon transfer of control of promised goods or services to customers in an amount that the Company expects to receive in exchange for those products or services. The Company determines revenue recognition through the following steps: • i dentification of the contract, or contracts, with a customer; • i dentification of the performance obligations in the contract; • d etermination of the transaction price; • a llocation of the transaction price to the performance obligations in the contract; and • r ecognition of revenue, when, or as, the Company satisfies a performance obligation. Nature of Products and Services Revenue consists primarily of the sale of communications services offered through Application Programming Interface (“API”) software solutions to large enterprise, as well as small and medium-sized business, customers and is generally derived from usage and service fees in both the CPaaS and Other segments. Usage revenue includes voice communication (primarily driven by inbound minutes, outbound minutes and toll-free minutes) and messaging communication (driven by the number of messages) that traverse the platform and network. Service fees include the provision and management of phone numbers and emergency services access. The majority of the Company ’ s revenue is generated from usage-based fees earned from customers accessing the Company ’ s communications platform. Access to the Company ’ s communication platform is considered a series of distinct services, with continuous transfer of control to the customer, comprising one performance obligation and usage-based fees are recognized in revenue in the period the traffic traverses the Company ’ s network. For the three months ended March 31, 2018, the revenue from usage-based fees represented $24,568 of CPaaS revenue and $12,164 of Other revenue. For the three months ended March 31, 2019, the revenue from usage-based fees represented $29,050 of CPaaS revenue and $6,792 of Other revenue. Revenue from service fees is recognized on a ratable basis as the service is provided, which is typically one month. For the three months ended March 31, 2018, the revenue from service fees represented $13,685 of CPaaS revenue and $1,951 of Other revenue. For the three months ended March 31, 2019, the revenue from service fees represented $14,754 of CPaaS revenue and $1,516 of Other revenue. The remaining $644 and $1,209 for the three months ended March 31, 2018 and 2019, respectively, are generated from other miscellaneous services. Infrequently, Bandwidth ’ s contracts with customers may include multiple performance obligations. For such arrangements, revenues are allocated to each performance obligation based on its relative standalone selling price. Generally, standalone selling prices are determined based on the prices charged to similar customers for similar services. When required as part of providing service, revenues and associated expenses related to nonrefundable, upfront service activation and setup fees are deferred and recognized over the longer of the associated service contract period or estimated customer life. The Company ’ s contracts do not contain general rights of return. However, occasionally credits may be issued. The Company ’ s contracts do not provide customers with the right to take possession of the software supporting the applications. Amounts that have been invoiced are recorded in accounts receivable and in revenue or deferred revenue depending on whether the revenue recognition criteria have been met. The Company maintains a reserve for sales credits. Credits are accounted for as variable consideration and are estimated based on several inputs including historical experience and current trends of credit issuances. Adjustments to the reserve are recorded against revenue. The Company has various sales commission plans for which eligible employees can earn commissions from the sale of products and services to customers. Eligible employees must be employed at the time of payment in order to receive a commission. The Company pays commissions over time and a corresponding requisite substantive service condition exists for the employee to receive the commission. The Company determined that the timing of the commission payments and the underlying service performed by the employee were commensurate. Accordingly, sales commissions are generally expensed as incurred. These costs are recorded within sales and marketing expenses. Contract Assets and Liabilities The following table provides information about receivables and contract liabilities from contracts with customers: March 31, 2019 Receivables (1) $ 27,898 Contract liabilities (2) 11,780 ________________________ (1) Included in accounts receivable, net of allowance on the consolidated balance sheet. (2) Included in current portion of deferred revenue and deferred revenue, net of current portion on the consolidated balance sheet. Deferred revenue is recorded when cash payments are received in advance of future usage on contracts. Customer refundable payments are recorded as advanced billings. Revenue is typically recognized in the month following when service is rendered or, in the case of nonrefundable upfront fees, over the estimated period of benefit. During the three months ended March 31, 2019, the Company recognized revenue of $2,218, related to its contract liabilities. The Company expects to recognize $5,421 in revenue over the next twelve months related to its deferred revenue as of March 31, 2019.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In October 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-17, Consolidation (Topic 810), Targeted Improvements to Related Party Guidance for Variable Interest Entities , which addresses the cost and complexity of financial reporting associated with consolidation of variable interest entities (“VIE”). ASU 2018-17 is effective for emerging growth companies following private company adoption dates in fiscal years beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020, with early adoption permitted. The new guidance must be applied on a retrospective basis as a cumulative-effect adjustment as of the date of adoption. Management does not expect the adoption of this guidance to have a significant impact on the Company’s financial statements. In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract . This standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 is effective for emerging growth companies following private company adoption dates in fiscal years beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates certain disclosure requirements for fair value measurements for all entities, requires public entities to disclose certain new information and modifies some disclosure requirements. ASU 2018-13 is effective for all entities for fiscal years beginning after December 15, 2019 and for interim periods within those fiscal years, and early adoption is permitted. An entity is permitted to early adopt either the entire standard or only the provisions that eliminate or modify requirements. 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 public business entities that are U.S. SEC filers 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 statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments–Credit Losses: Measurement of Credit Losses on Financial Instruments , which changes the impairment model for most financial assets. The new model uses a forward-looking expected loss method, which will generally result in earlier recognition of allowances for losses. In November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments – Credit Losses , which clarifies that receivables arising from operating leases are not within the scope of Topic 326, Financial Instruments – Credit Losses. Instead, impairment of receivables arising from operating leases should be accounted for in accordance with Topic 842, Leases. These ASUs are effective for public business entities that are SEC filers for annual and interim periods beginning after December 15, 2019 and early adoption is permitted for annual and interim periods beginning after December 15, 2018. The Company is evaluating the impact of this guidance on its consolidated financial statements. 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. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, Leases, to clarify how to apply certain aspects of the new leases standard. In July 2018, the FASB also issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, to give entities another option for transition and to provide lessors with a practical expedient to reduce the cost and complexity of implementing the new standard. The transition option allows entities to not apply the new leases standard in the comparative periods they present in their financial statements in the year of adoption. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements, to clarify how to apply certain aspects of the new lease standard. ASU 2016-02 is effective for emerging growth companies following private company adoption dates in 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.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents, and 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, 2018 2019 Cash and cash equivalents $ 41,261 $ 138,871 Restricted cash 240 224 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 41,501 $ 139,095
Reconciliation of Cash, Cash Equivalents, and 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, 2018 2019 Cash and cash equivalents $ 41,261 $ 138,871 Restricted cash 240 224 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 41,501 $ 139,095
Information about Receivables and Contract Liabilities from Contract with Customers	The following table provides information about receivables and contract liabilities from contracts with customers: March 31, 2019 Receivables (1) $ 27,898 Contract liabilities (2) 11,780 ________________________ (1) Included in accounts receivable, net of allowance on the consolidated balance sheet. (2) Included in current portion of deferred revenue and deferred revenue, net of current portion on the consolidated balance sheet.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
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, 2018 and March 31, 2019: Amortized cost or carrying value Unrealized gains Unrealized losses Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 8,194 $ — $ — $ 8,194 $ — $ — $ 8,194 U.S. Reverse repurchase agreements 26,000 — — — 26,000 — 26,000 Total included in cash and cash equivalents 34,194 — — 8,194 26,000 — 34,194 Marketable securities: U.S. treasury securities 17,402 — (2) 17,400 — — 17,400 Total marketable securities 17,402 — (2) 17,400 — — 17,400 Total financial assets $ 51,596 $ — $ (2) $ 25,594 $ 26,000 $ — $ 51,594 Amortized cost or carrying value Unrealized gains Unrealized losses Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 17,380 $ — $ — $ 17,380 $ — $ — $ 17,380 U.S. Reverse repurchase agreements 115,000 — — — 115,000 — 115,000 Total included in cash and cash equivalents 132,380 — — 17,380 115,000 — 132,380 Marketable securities: U.S. treasury securities 59,509 11 — 59,520 — — 59,520 Total marketable securities 59,509 11 — 59,520 — — 59,520 Total financial assets $ 191,889 $ 11 $ — $ 76,900 $ 115,000 $ — $ 191,900
Schedule of Contractual Maturities of Marketable Securities	The following table summarizes the contractual maturities of marketable securities as of March 31, 2019: Amortized cost Aggregate fair value Financial assets: Less than one year $ 59,509 $ 59,520 Total $ 59,509 $ 59,520

Financial Statement Components

Financial Statement Components (Tables)	3 Months Ended
	Mar. 31, 2019
Financial Statement Components [Abstract]
Schedule of Accounts Receivable, net of Allowance for Doubtful Accounts	Accounts receivable, net of allowance for doubtful accounts consist of the following: December 31, March 31, 2018 2019 Trade accounts receivable $ 13,620 $ 15,559 Unbilled accounts receivable 11,174 13,231 Allowance for doubtful accounts (906) (1,018) Other accounts receivable 121 126 Total accounts receivable, net $ 24,009 $ 27,898 Components of allowance for doubtful accounts are as follows: Three months ended March 31, Allowance for doubtful accounts: 2018 2019 Balance, beginning of period $ (32,463) $ (906) Charged to bad debt expense (1) (132) Deductions (1) 56 20 Billings deemed not probable of collection (2) (118) — Write-off of previously outstanding and fully reserved billings related to settlement (3) 24,968 — Revenue recognized from outstanding billings previously deemed uncollectible related to settlement (3) 6,268 — Balance, end of period $ (1,290) $ (1,018) ________________________ (1) Write off of uncollectible accounts after all collection efforts have been exhausted. (2) Represents amounts billed in the period but where collectability is not probable based on customers collection experience. Amounts were charged to a contra-revenue account. (3) 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. Immediately following receipt of the $4,400 payment, the Company issued to Verizon bill credits with respect to other CABS amounts previously billed and reserved to Verizon of $24,968. The amount credited to Verizon comprised the majority of the allowance for CABS revenue as of December 31, 2017. 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 and the other current outstanding Verizon CABS receivables which had been previously reserved as uncollectible, but for which collection was no longer in doubt as a result of the settlement. The settlement agreement also specifies certain terms for the Company’s CABS billings to Verizon prospectively.
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: December 31, March 31, 2018 2019 Accrued expense $ 8,292 $ 11,440 Accrued compensation and benefits 7,323 4,337 Accrued sales, use, and telecom related taxes 4,742 5,074 Deferred rent, current portion 298 123 Other accrued expenses 738 794 Total accrued expenses and other current liabilities $ 21,393 $ 21,768

Property and Equipment (Tables)

Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following: December 31, March 31, 2018 2019 Furniture and fixtures $ 1,741 $ 1,793 Computer and office equipment 7,662 7,827 Telecommunications equipment 30,694 31,170 Leasehold improvements 2,438 2,388 Software development costs 16,293 18,728 Automobile 10 10 Total cost 58,838 61,916 Less—accumulated depreciation (33,702) (35,553) Total property and equipment, net $ 25,136 $ 26,363
Schedule of Depreciation Expense	The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows: Three months ended March 31, 2018 2019 Cost of revenue $ 1,064 $ 1,293 Research and development 29 69 Sales and marketing 10 28 General and administrative 119 689 Total depreciation expense $ 1,222 $ 2,079

Intangible Assets (Tables)

Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	Intangible assets, net consisted of the following as of December 31, 2018: Gross Accumulated Net Carrying Amortization (Years) Customer relationships $ 10,396 $ (4,071) $ 6,325 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 $ (8,004) $ 7,089 Intangible assets, net consisted of the following as of March 31, 2019: Gross Accumulated Net Carrying Amortization (Years) Customer relationships $ 10,396 $ (4,201) $ 6,195 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 $ (8,134) $ 6,959
Schedule of Future Estimated Amortization Expense	Future estimated amortization expense for definite lived intangible assets is as follows: As of March 31, 2019 2019 (remaining) $ 390 2020 520 2021 520 2022 520 2023 520 Thereafter 3,725 $ 6,195

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Three months ended March 31, 2018 2019 CPaaS Revenue $ 38,897 $ 45,013 Cost of revenue 21,905 25,300 Gross profit $ 16,992 $ 19,713 Other Revenue $ 14,115 $ 8,308 Cost of revenue 3,459 3,466 Gross profit $ 10,656 $ 4,842 Consolidated Revenue $ 53,012 $ 53,321 Cost of revenue 25,364 28,766 Gross profit $ 27,648 $ 24,555
Schedule of Revenue by Geographical Area	The Company generates its revenue primarily in the United States. Revenue by geographic area is detailed in the table below (which is determined based on the customer billing address): Three months ended March 31, 2018 2019 CPaaS United States $ 38,779 $ 44,944 International 118 69 Total $ 38,897 $ 45,013 Other United States $ 14,045 $ 8,229 International 70 79 Total $ 14,115 $ 8,308

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Schedule of Reserved Shares of Common Stock for Issuance	The Company had reserved shares of Class A common stock for issuance as follows: December 31, March 31, 2018 2019 Stock options issued and outstanding 1,937,370 1,346,119 Nonvested restricted stock units issued and outstanding 324,252 432,240 Stock-based awards available for grant under the 2017 Plan 896,760 1,329,042 3,158,382 3,107,401

Stock Based Compensation (Table

Stock Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Activity	The following summarizes the stock option activity for the periods presented: Number of Weighted- Weighted- Aggregate Outstanding as of December 31, 2018 1,937,370 $ 7.41 4 $ 64,596 Granted — — Exercised (589,510) 6.68 23,804 Forfeited or cancelled (1,741) 11.91 Outstanding as of March 31, 2019 1,346,119 $ 7.72 3.89 $ 79,740 Options vested and exercisable at March 31, 2019 1,107,396 $ 6.69 3.11 $ 66,741 Options vested and expected to vest as of March 31, 2019 1,341,197 $ 7.70 3.87 $ 79,477
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) Nonvested RSUs as of December 31, 2018 324,252 $ 26.95 Granted 214,915 41.42 Vested (105,367) 28.07 Forfeited or cancelled (1,560) 35.06 Nonvested RSUs as of March 31, 2019 432,240 $ 33.84
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, 2018 2019 Cost of revenue $ 18 $ 56 Research and development 74 372 Sales and marketing 78 320 General and administrative 323 928 Total $ 493 $ 1,676

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Operating Leases	Future minimum lease payments required under operating leases are as follows: As of March 31, 2019 2019 (remaining) $ 4,402 2020 6,342 2021 6,497 2022 6,210 2023 5,833 Thereafter 2,848 $ 32,132
Schedule of Future Minimum Lease Receipts for Operating Lease	Future minimum sub-lease receipts required under the non-cancellable lease are as follows: As of March 31, 2019 2019 (remaining) $ 785 2020 1,065 2021 1,089 2022 594 $ 3,533

Basic and Diluted Income per _2

Basic and Diluted Income per Common Share (Tables)	3 Months Ended
	Mar. 31, 2019
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, 2018 2019 Earnings per share Net income attributable to common stockholders $ 6,191 $ 1,992 Net income per share: Basic $ 0.35 $ 0.10 Diluted $ 0.30 $ 0.09 Weighted Average Number of Common Shares Outstanding Basic 17,658,611 20,498,104 Dilutive effect of stock options, restricted stock units, and warrants 2,826,142 1,477,840 Diluted 20,484,753 21,975,944
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, 2018 2019 Anti-dilutive Disclosure Stock options issued and outstanding 94,126 —

Organization and Description _2

Organization and Description of Business (Details) $ / shares in Units, $ in Thousands	Mar. 11, 2019USD ($)$ / sharesshares	Mar. 31, 2019segment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of operating segments | segment		2
Number of reportable segments | segment		2
Proceeds from follow-on public offering | $	$ 146,597
Follow-on Public Offering | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares) | shares	2,875,000
Shares issued, price (in usd per share) | $ / shares	$ 54.25
Over-Allotment Option | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares) | shares	375,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jan. 01, 2019
Accounting Policies [Abstract]
RRAs collateralized by deposits in form of Government Securities and Obligations as percentage of value	102.00%
Concentration Risk [Line Items]
Adjustment to opening retained earnings due to adoption of ASC 606			$ 174
Revenue	$ 53,321	$ 53,012
Revenue recognized related to its contract liabilities	$ 2,218
Customer One | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk percentage	16.00%		18.00%
Retained earnings
Concentration Risk [Line Items]
Adjustment to opening retained earnings due to adoption of ASC 606			$ 174
Accounting Standards Update 2014-09 | Retained earnings
Concentration Risk [Line Items]
Adjustment to opening retained earnings due to adoption of ASC 606				$ 174
CPaaS, Usage-Based Fees
Concentration Risk [Line Items]
Revenue	$ 29,050	24,568
Other, Usage-Based Fees
Concentration Risk [Line Items]
Revenue	6,792	12,164
CPaaS, Service Fees
Concentration Risk [Line Items]
Revenue	14,754	13,685
Other, Service Fees
Concentration Risk [Line Items]
Revenue	1,516	1,951
Other miscellaneous services
Concentration Risk [Line Items]
Revenue	$ 1,209	$ 644

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Remaining Performance Obligation (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01 $ in Thousands	Mar. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 5,421
Revenue, remaining performance obligation, amount, expected timing of satisfaction, period	12 months

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 138,871	$ 41,261
Restricted cash	224	240
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 139,095	$ 41,501	$ 38,973	$ 37,870

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Information about Receivables and Contract Liabilities from Contract with Customers (Details) $ in Thousands	Mar. 31, 2019USD ($)
Accounting Policies [Abstract]
Receivables	$ 27,898
Contract liabilities	$ 11,780

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, amortized cost or carrying value	$ 138,871	$ 41,261
Marketable securities, amortized cost or carrying value	59,509	17,402
Marketable securities, unrealized gain	11	0
Marketable securities, net unrealized losses	0	(2)
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	17,380	8,194
Cash and cash equivalents, unrealized gains	0	0
Cash and cash equivalents, unrealized loss	0	0
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	115,000	26,000
Cash and cash equivalents, unrealized gains	0	0
Cash and cash equivalents, unrealized loss	0	0
Financial assets excluding marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, amortized cost or carrying value	132,380	34,194
Cash and cash equivalents, unrealized gains	0	0
Cash and cash equivalents, unrealized loss	0	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	59,509	17,402
Marketable securities, unrealized gain	11	0
Marketable securities, net unrealized losses	0	(2)
Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value	191,889	51,596
Financial assets, unrealized gain	11	0
FinancialAssetsGrossUnrealizedLoss	0	(2)
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	59,520	17,400
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	17,380	8,194
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	115,000	26,000
Fair Value, Measurements, Recurring | Financial assets excluding marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	132,380	34,194
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	59,520	17,400
Fair Value, Measurements, Recurring | Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value	191,900	51,594
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	59,520	17,400
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	17,380	8,194
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	0
Level 1 | Fair Value, Measurements, Recurring | Financial assets excluding marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	17,380	8,194
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	59,520	17,400
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	76,900	25,594
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	0	0
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	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	115,000	26,000
Level 2 | Fair Value, Measurements, Recurring | Financial assets excluding marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	115,000	26,000
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	0	0
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	115,000	26,000
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, fair value	0	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	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	0
Level 3 | Fair Value, Measurements, Recurring | Financial assets excluding marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0	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	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	$ 0

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Contractual Maturities of Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost	$ 59,509
Aggregate fair value	59,520
Maturities of marketable securities	9,000	$ 0
Interest earned on marketable securities	3	$ 16
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost	59,509
Aggregate fair value	$ 59,520

Financial Statement Component_2

Financial Statement Components - Accounts Receivable, Net of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Statement Components [Abstract]
Trade accounts receivable	$ 15,559	$ 13,620
Unbilled accounts receivable	13,231	11,174
Allowance for doubtful accounts	(1,018)	(906)
Other accounts receivable	126	121
Total accounts receivable, net	$ 27,898	$ 24,009

Financial Statement Component_3

Financial Statement Components - Allowance For Doubtful Accounts (Details) - USD ($) $ in Thousands	Feb. 08, 2018	Mar. 31, 2019	Mar. 31, 2018
Carrier Access Billing (CAB)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Settlement agreement lump sum payment	$ 4,400
Accounts Receivable, Excluding Carrier Access Billing (CAB)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period		$ (906)	$ (32,463)
Charged to bad debt expense		(132)	(1)
Deductions		20	56
Billings deemed not probable of collection		0	(118)
Balance, end of period		(1,018)	(1,290)
Carrier Access Billing (CAB)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Write-off of previously outstanding and fully reserved billings related to settlement		0	24,968
Revenue recognized as a result of settlement agreement		$ 0	$ 6,268

Financial Statement Component_4

Financial Statement Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Statement Components [Abstract]
Accrued expense	$ 11,440	$ 8,292
Accrued compensation and benefits	4,337	7,323
Accrued sales, use, and telecom related taxes	5,074	4,742
Deferred rent, current portion	123	298
Other accrued expenses	794	738
Total accrued expenses and other current liabilities	$ 21,768	$ 21,393

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total cost	$ 61,916	$ 58,838
Less—accumulated depreciation	(35,553)	(33,702)
Total property and equipment, net	26,363	25,136
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total cost	1,793	1,741
Computer and office equipment
Property, Plant and Equipment [Line Items]
Total cost	7,827	7,662
Telecommunications equipment
Property, Plant and Equipment [Line Items]
Total cost	31,170	30,694
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total cost	2,388	2,438
Software development costs
Property, Plant and Equipment [Line Items]
Total cost	18,728	16,293
Automobile
Property, Plant and Equipment [Line Items]
Total cost	$ 10	$ 10

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Capitalized software development costs, additions	$ 595	$ 441
Amortization of capitalized software development costs	$ 789	$ 448

Property and Equipment - Deprec

Property and Equipment - Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Depreciation Expense [Line Items]
Depreciation	$ 2,079	$ 1,222
Cost of revenue
Depreciation Expense [Line Items]
Depreciation	1,293	1,064
Research and development
Depreciation Expense [Line Items]
Depreciation	69	29
Sales and marketing
Depreciation Expense [Line Items]
Depreciation	28	10
General and administrative
Depreciation Expense [Line Items]
Depreciation	$ 689	$ 119

Intangible Assets - Summary of

Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (8,134)	$ (8,004)
Finite-lived intangible assets, net	6,195
Gross amount	15,093	15,093
Net carrying value	6,959	7,089
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	(4,201)	(4,071)
Finite-lived intangible assets, net	$ 6,195	$ 6,325
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)	(2,678)
Finite-lived intangible assets, net	$ 0	$ 0
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

Intangible Assets - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 130	$ 165
Weighted average amortization period	12 years

Intangible Assets - Future Esti

Intangible Assets - Future Estimated Amortization Expense (Details) $ in Thousands	Mar. 31, 2019USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2019 (remaining)	$ 390
2020	520
2021	520
2022	520
2023	520
Thereafter	3,725
Finite-lived intangible assets, net	$ 6,195

Debt (Details)

Debt (Details) - USD ($)	Mar. 01, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt instrument, term	3 years
Cost of assets under capital leases		$ 1,951,000	$ 1,951,000
Accumulated depreciation of assets under capital leases		1,889,000	1,884,000
Remaining payments due on capital lease		0
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25,000,000
Debt outstanding		0	0
Available borrowing capacity		25,000,000
Outstanding unamortized loan fees		$ 138,000	$ 136,000
Interest expense	125,000
Letters of credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	2,500,000
Swing line
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,000,000
Federal Funds Effective Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%

Segment and Geographic Inform_3

Segment and Geographic Information - Reconciliation of Segment Profit (Loss) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)segment	Mar. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2
Revenue	$ 53,321	$ 53,012
Cost of revenue	28,766	25,364
Gross profit	24,555	27,648
CPaaS
Segment Reporting Information [Line Items]
Revenue	45,013	38,897
Cost of revenue	25,300	21,905
Gross profit	19,713	16,992
Other
Segment Reporting Information [Line Items]
Revenue	8,308	14,115
Cost of revenue	3,466	3,459
Gross profit	$ 4,842	$ 10,656

Segment and Geographic Inform_4

Segment and Geographic Information - Reconciliation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 53,321	$ 53,012
CPaaS
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	45,013	38,897
CPaaS | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	44,944	38,779
CPaaS | International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	69	118
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	8,308	14,115
Other | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	8,229	14,045
Other | International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 79	$ 70

Stockholder's Equity - Preferre

Stockholder's Equity - Preferred Stock (Details) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0

Stockholder's Equity - Common S

Stockholder's Equity - Common Stock (Details)	Mar. 31, 2019vote$ / sharesshares	Dec. 31, 2018vote$ / sharesshares
Common Class A
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock voting rights, votes per share | vote	1	1
Common stock, shares issued (in shares)	16,523,269	12,912,747
Common stock, shares outstanding (in shares)	16,523,269	12,912,747
Common stock, par value (in usd per share) | $ / shares	$ 0.001	$ 0.001
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 | vote	10	10
Common stock, shares issued (in shares)	6,453,502	6,510,732
Common stock, shares outstanding (in shares)	6,453,502	6,510,732

Stockholders' Equity - Reserved

Stockholders' Equity - Reserved Shares of Common Stock for Issuance (Details) - shares	Mar. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	3,107,401	3,158,382
Stock options issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	1,346,119	1,937,370
Nonvested restricted stock units issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	432,240	324,252
Stock-based awards available for grant under the 2017 Plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	1,329,042	896,760

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2019	Jan. 01, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Nov. 09, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)			3,107,401		3,158,382
Estimated grant date fair value of options vested			$ 57	$ 111
Unrecognized cost for stock based compensation			1,012
Unrecognized compensation cost related to non-vested RSUs			$ 14,118
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized cost for stock based compensation, period for recognition (in years)			1 year 10 months 13 days
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)			432,240		324,252
Vesting percentage			25.00%
Share-based compensation arrangement, requisite service period			4 years
Unrecognized cost for stock based compensation, period for recognition (in years)			3 years 4 months 13 days
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)	645,637
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
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
Executives | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			4 years
Tranche One | Executives | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			50.00%
Tranche Two | Executives | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%
Tranche Three | Executives | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%
Tranche Four | Executives | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%

Stock Based Compensation - Stoc

Stock Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options vested and expected to vest (in shares)	1,341,197
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price, options vested and expected to vest (in usd per share)	$ 7.70
Weighted average remaining contract life, options vested and expected to vest	3 years 10 months 13 days
Aggregate intrinsic value, options vested and expected to vest	$ 79,477
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options outstanding, beginning balance (in shares)	1,937,370
Number of options, granted (in shares)	0
Number of options exercised (in shares)	(589,510)
Number of options, forfeited or cancelled (in shares)	(1,741)
Number of options outstanding, ending balance (in shares)	1,346,119	1,937,370
Number of options outstanding, options vested and exercisable (in shares)	1,107,396
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)	$ 7.41
Weighted-average exercise price, granted (in usd per share)	0
Weighted-average exercise price, exercised (in usd per share)	6.68
Weighted-average exercise price, forfeited or cancelled (in usd per share)	11.91
Weighted-average exercise price, ending balance (in usd per share)	7.72	$ 7.41
Weighted-average exercise price, options vested and exercisable (in usd per share)	$ 6.69
Weighted-average remaining contract life, options outstanding (in years)			3 years 10 months 20 days	4 years
Weighted-average remaining contract life, options vested and exercisable (in years)			3 years 1 month 9 days
Aggregate intrinsic value, options outstanding	$ 79,740	$ 64,596
Aggregate intrinsic value, options exercised	23,804
Aggregate intrinsic value, options vested and exercisable	$ 66,741

Stock Based Compensation - Rest

Stock Based Compensation - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs)	3 Months Ended
	Mar. 31, 2019$ / sharesshares
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) | shares	324,252
Number of nonvested RSUs, granted (in shares) | shares	214,915
Number of nonvested RSUs, vested (in shares) | shares	(105,367)
Number of nonvested RSUs, forfeited or cancelled (in shares) | shares	(1,560)
Number of nonvested RSUs outstanding, ending balance (in shares) | shares	432,240
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) | $ / shares	$ 26.95
Weighted average grant-date fair value of nonvested RSUS, granted (in usd per share) | $ / shares	41.42
Weighted-average grant date fair value of nonvested RSUs, vested (in usd per share) | $ / shares	28.07
Weighted-average grant date fair value of nonvested restricted RSUs, forfeited or cancelled (in usd per share) | $ / shares	35.06
Weighted-average grant date fair value, ending balance (in usd per share) | $ / shares	$ 33.84

Stock Based Compensation - St_2

Stock Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,676	$ 493
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	56	18
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	372	74
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	320	78
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 928	$ 323

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	Oct. 25, 2015USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Jan. 01, 2019ft²	Nov. 30, 2016ft²
Lessee, Lease, Description [Line Items]
Rent expense		$ 1,218	$ 933
Service agreement, annual minimum commitments	$ 1,200
Service agreement, term of agreement (in years)	5 years
Non-cancellable purchase obligation		6,353
Non-cancellable purchase obligation, fulfilled within a year		5,448
General and administrative
Lessee, Lease, Description [Line Items]
Reduction of rent expense		$ 251	$ 251
Raleigh, NC
Lessee, Lease, Description [Line Items]
Office space (in square foot) | ft²				117,719
Increase of office space (in square foot) | ft²				30,114
Lessee, operating lease, renewal term				5 years
Spin-off
Lessee, Lease, Description [Line Items]
Office space (in square foot) | ft²					40,657
Lessee, operating lease, renewal term				5 years
Lessee, operating lease, additional renewal term		18 months

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Rental Payments for Operating Leases (Details) $ in Thousands	Mar. 31, 2019USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019 (remaining)	$ 4,402
2020	6,342
2021	6,497
2022	6,210
2023	5,833
Thereafter	2,848
Future minimum payments due, total	$ 32,132

Commitments and Contingencies_3

Commitments and Contingencies - Future Minimum Lease Receipts (Details) $ in Thousands	Mar. 31, 2019USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019 (remaining)	$ 785
2020	1,065
2021	1,089
2022	594
Future minimum lease receipts, total	$ 3,533

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Matching contributions	$ 513	$ 287

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Effective tax rate	135.20%	29.80%

Related Parties (Details)

Related Parties (Details) - Affiliated Entity - Republic - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Amount collected on behalf	$ 613,000
Due to related parties	0
Transition Services Agreement
Related Party Transaction [Line Items]
Revenue from related parties	0	$ 28,000
Accounts receivable, related parties	0		$ 0
Facilities Sharing Agreement
Related Party Transaction [Line Items]
Rental payments received	251,000	251,000
Due from related parties	0		0
Tax Sharing Agreement
Related Party Transaction [Line Items]
Due from related parties	0		0
Master Services Agreement
Related Party Transaction [Line Items]
Revenue from related parties	892,000	$ 986,000
Accounts receivable, related parties	$ 284,000		$ 310,000

Basic and Diluted Income per _3

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, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$ 1,992	$ 6,191
Net income per share:
Basic (in usd per share)	$ 0.10	$ 0.35
Diluted (in usd per share)	$ 0.09	$ 0.30
Weighted Average Number of Common Shares Outstanding
Basic (in shares)	20,498,104	17,658,611
Dilutive effect of stock options, restricted stock units, and warrants (in shares)	1,477,840	2,826,142
Diluted (in shares)	21,975,944	20,484,753

Basic and Diluted Income per _4

Basic and Diluted Income per Common Share - Antidilutive Securities Excluded from the Computation (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
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 (in shares)	0	94,126