Bandwidth (BAND) 10-Q 9 Nov 21 2021 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-38285
Entity Registrant Name	BANDWIDTH INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	56-2242657
Entity Address, Address Line One	900 Main Campus Drive
Entity Address, City or Town	Raleigh
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27606
City Area Code	(800)
Local Phone Number	808-5150
Title of 12(b) Security	Class A Common Stock, par value $0.001 per share
Trading Symbol	BAND
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0001514416
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
Class A voting common stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		23,168,711
Class B voting common stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,965,170

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 321,819	$ 72,163
Restricted cash	9,239	9,274
Other investments	0	40,000
Accounts receivable, net of allowance for doubtful accounts	75,161	55,243
Deferred costs	2,951	2,411
Prepaid expenses and other current assets	22,355	14,508
Total current assets	431,525	193,599
Property, plant and equipment, net	68,267	51,645
Operating right-of-use asset, net	15,612	19,491
Intangible assets, net	220,566	248,055
Deferred costs, non-current	4,262	3,604
Other long-term assets	7,543	1,975
Goodwill	353,151	372,239
Total assets	1,100,926	890,608
Current liabilities:
Accounts payable	15,688	11,665
Accrued expenses and other current liabilities	76,259	63,065
Current portion of deferred revenue	6,362	6,515
Advanced billings	4,797	5,429
Operating lease liability, current	6,015	5,515
Total current liabilities	109,121	92,189
Other liabilities	5,416	1,707
Operating lease liability, net of current portion	12,525	17,202
Deferred revenue, net of current portion	7,383	6,386
Deferred tax liability	57,997	61,005
Convertible senior notes	479,155	282,196
Total liabilities	671,597	460,685
Stockholders’ equity:
Class A and Class B common stock	25	24
Additional paid-in capital	499,738	451,463
Accumulated deficit	(68,693)	(49,505)
Accumulated other comprehensive income (loss)	(1,741)	27,941
Total stockholders’ equity	429,329	429,923
Total liabilities and stockholders’ equity	$ 1,100,926	$ 890,608

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 130,638	$ 84,758	$ 364,775	$ 230,066
Cost of revenue	72,395	45,527	199,782	123,895
Gross profit	58,243	39,231	164,993	106,171
Operating expenses:
Research and development	13,359	10,232	39,509	29,316
Sales and marketing	13,592	9,001	38,168	27,073
General and administrative	30,354	18,134	85,481	51,070
Total operating expenses	57,305	37,367	163,158	107,459
Operating income (loss)	938	1,864	1,835	(1,288)
Other expense, net	(7,567)	(4,206)	(20,768)	(8,980)
Loss before income taxes	(6,629)	(2,342)	(18,933)	(10,268)
Income tax provision	(315)	(10)	(255)	(13,783)
Net loss	$ (6,944)	$ (2,352)	$ (19,188)	$ (24,051)
Net loss per share, basic (in usd per share)	$ (0.28)	$ (0.10)	$ (0.77)	$ (1.01)
Net loss per share, diluted (in usd per share)	$ (0.28)	$ (0.10)	$ (0.77)	$ (1.01)
Weighted average number of common shares outstanding, basic (in shares)	25,114,762	24,175,762	25,075,941	23,905,322
Weighted average number of common shares outstanding, diluted (in shares)	25,114,762	24,175,762	25,075,941	23,905,322

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (6,944)	$ (2,352)	$ (19,188)	$ (24,051)
Other comprehensive income (loss)
Foreign currency translation, net of income taxes	(12,512)	139	(29,682)	20
Other comprehensive income (loss)	(12,512)	139	(29,682)	20
Total comprehensive loss	$ (19,456)	$ (2,213)	$ (48,870)	$ (24,031)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Stockholders’ Equity - USD ($) $ in Thousands	Total	Conversion of Class B voting common stock to Class A voting common stock	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 (loss) income	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2019					18,584,478		4,927,401
Beginning balance at Dec. 31, 2019	$ 270,090				$ 19		$ 5		$ 275,553	$ 41	$ (5,528)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of debt conversion option	104,553								104,553
Debt conversion option issuance costs, net of tax	(3,731)								(3,731)
Capped call option purchase price	(43,320)								(43,320)
Exercises of vested stock options (in shares)					32,059
Exercises of vested stock options	244								244
Vesting of restricted stock units (in shares)					103,824
Equity awards withheld for tax liability (in shares)					(14,411)
Equity awards withheld for tax liability	(1,021)								(1,021)
Conversion of Class B voting common stock to Class A voting common stock (in shares)						500,250		(500,250)
Conversion of Class B voting common stock to Class A voting common stock		$ (1)						$ (1)
Foreign currency translation	(96)									(96)
Stock based compensation	2,499								2,499
Net loss	(1,058)										(1,058)
Ending balance (in shares) at Mar. 31, 2020					19,206,200		4,427,151
Ending balance at Mar. 31, 2020	328,159				$ 19		$ 4		334,777	(55)	(6,586)
Beginning balance (in shares) at Dec. 31, 2019					18,584,478		4,927,401
Beginning balance at Dec. 31, 2019	270,090				$ 19		$ 5		275,553	41	(5,528)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(24,051)
Ending balance (in shares) at Sep. 30, 2020					21,222,929		2,993,136
Ending balance at Sep. 30, 2020	313,139				$ 21		$ 3		342,633	61	(29,579)
Beginning balance (in shares) at Mar. 31, 2020					19,206,200		4,427,151
Beginning balance at Mar. 31, 2020	328,159				$ 19		$ 4		334,777	(55)	(6,586)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Debt conversion option issuance costs, net of tax	(11)								(11)
Exercises of vested stock options (in shares)					502,182
Exercises of vested stock options	3,297				$ 1				3,296
Vesting of restricted stock units (in shares)					21,871
Equity awards withheld for tax liability (in shares)					(2,133)
Equity awards withheld for tax liability	(272)								(272)
Conversion of Class B voting common stock to Class A voting common stock (in shares)						827,597		(827,597)
Foreign currency translation	(23)									(23)
Stock based compensation	2,425								2,425
Net loss	(20,641)										(20,641)
Ending balance (in shares) at Jun. 30, 2020					20,555,717		3,599,554
Ending balance at Jun. 30, 2020	312,934				$ 20		$ 4		340,215	(78)	(27,227)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)					44,848
Exercises of vested stock options	386								386
Vesting of restricted stock units (in shares)					17,948
Equity awards withheld for tax liability (in shares)					(2,002)
Equity awards withheld for tax liability	(350)								(350)
Conversion of Class B voting common stock to Class A voting common stock (in shares)						606,418		(606,418)
Conversion of Class B voting common stock to Class A voting common stock		0				$ 1		$ (1)
Foreign currency translation	139									139
Stock based compensation	2,382								2,382
Net loss	(2,352)										(2,352)
Ending balance (in shares) at Sep. 30, 2020					21,222,929		2,993,136
Ending balance at Sep. 30, 2020	313,139				$ 21		$ 3		342,633	61	(29,579)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)					13,995
Exercises of vested stock options	149								149
Vesting of restricted stock units (in shares)					17,424
Equity awards withheld for tax liability (in shares)					(1,749)
Equity awards withheld for tax liability	(273)								(273)
Conversion of Class B voting common stock to Class A voting common stock (in shares)						497,011		(497,011)
Conversion of Class B voting common stock to Class A voting common stock		(1)						$ (1)
Equity consideration for Voxbone acquisition (in shares)					663,394
Equity consideration for Voxbone acquisition	106,380				$ 1				106,379
Foreign currency translation	27,880									27,880
Stock based compensation	2,575								2,575
Net loss	(19,926)										(19,926)
Ending balance (in shares) at Dec. 31, 2020			22,413,004	2,496,125	22,413,004		2,496,125
Ending balance at Dec. 31, 2020	429,923				$ 22		$ 2		451,463	27,941	(49,505)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of debt conversion option	66,908								66,908
Debt conversion option issuance costs, net of tax	(2,049)								(2,049)
Capped call option purchase price	(25,500)								(25,500)
Exercises of vested stock options (in shares)					57,817
Exercises of vested stock options	753								753
Vesting of restricted stock units (in shares)					141,707
Equity awards withheld for tax liability (in shares)					(19,879)
Equity awards withheld for tax liability	(3,187)								(3,187)
Conversion of Class B voting common stock to Class A voting common stock (in shares)						280,955		(280,955)
Conversion of Class B voting common stock to Class A voting common stock		$ 1				$ 1
Foreign currency translation	(23,185)									(23,185)
Stock based compensation	4,390								4,390
Net loss	(5,316)										(5,316)
Ending balance (in shares) at Mar. 31, 2021					22,873,604		2,215,170
Ending balance at Mar. 31, 2021	442,738				$ 23		$ 2		492,778	4,756	(54,821)
Beginning balance (in shares) at Dec. 31, 2020			22,413,004	2,496,125	22,413,004		2,496,125
Beginning balance at Dec. 31, 2020	429,923				$ 22		$ 2		451,463	27,941	(49,505)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(19,188)
Ending balance (in shares) at Sep. 30, 2021			23,165,119	1,965,170	23,165,119		1,965,170
Ending balance at Sep. 30, 2021	429,329				$ 23		$ 2		499,738	(1,741)	(68,693)
Beginning balance (in shares) at Mar. 31, 2021					22,873,604		2,215,170
Beginning balance at Mar. 31, 2021	442,738				$ 23		$ 2		492,778	4,756	(54,821)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Debt conversion option issuance costs, net of tax	30								30
Exercises of vested stock options (in shares)					4,406
Exercises of vested stock options	46								46
Vesting of restricted stock units (in shares)					15,605
Equity awards withheld for tax liability (in shares)					(1,948)
Equity awards withheld for tax liability	(265)								(265)
Foreign currency translation	6,015									6,015
Stock based compensation	3,377								3,377
Net loss	(6,928)										(6,928)
Ending balance (in shares) at Jun. 30, 2021					22,891,667		2,215,170
Ending balance at Jun. 30, 2021	445,013				$ 23		$ 2		495,966	10,771	(61,749)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of vested stock options (in shares)					8,700
Exercises of vested stock options	101								101
Vesting of restricted stock units (in shares)					16,383
Equity awards withheld for tax liability (in shares)					(1,631)
Equity awards withheld for tax liability	(154)								(154)
Conversion of Class B voting common stock to Class A voting common stock (in shares)						250,000		(250,000)
Foreign currency translation	(12,512)									(12,512)
Stock based compensation	3,825								3,825
Net loss	(6,944)										(6,944)
Ending balance (in shares) at Sep. 30, 2021			23,165,119	1,965,170	23,165,119		1,965,170
Ending balance at Sep. 30, 2021	$ 429,329				$ 23		$ 2		$ 499,738	$ (1,741)	$ (68,693)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (19,188)	$ (24,051)
Adjustments to reconcile net loss to net cash provided by operating activities
Depreciation and amortization	27,478	9,927
Right-of-use asset amortization	4,251	3,522
Amortization of debt discount and issuance costs	19,475	10,916
Stock-based compensation	11,592	7,306
Deferred taxes	329	14,254
Loss on disposal of property and equipment	357	263
Changes in operating assets and liabilities:
Accounts receivable, net of allowances	(20,610)	(16,218)
Prepaid expenses and other assets	(4,173)	(2,224)
Accounts payable	7,122	2,905
Accrued expenses and other liabilities	1,590	8,675
Operating right-of-use liability	(4,535)	(3,944)
Net cash (used in) provided by operating activities	23,688	11,331
Cash flows from investing activities
Purchase of property and equipment	(12,552)	(9,536)
Capitalized software development costs	(3,212)	(1,846)
Purchase of land	(30,017)	0
Proceeds from sale of land	17,462	0
Purchase of other investments	0	(230,780)
Proceeds from sales and maturities of other investments	40,000	0
Net cash (used in) provided by investing activities	11,681	(242,162)
Cash flows from financing activities
Payments on finance leases	(161)	0
Proceeds from issuance of convertible senior notes	250,000	400,000
Purchase of capped call	(25,500)	(43,320)
Payment of debt issuance costs	(7,544)	(11,965)
Proceeds from exercises of stock options	886	3,859
Value of equity awards withheld for tax liabilities	(3,720)	(1,472)
Net cash provided by financing activities	213,961	347,102
Effect of exchange rate changes on cash, cash equivalents and restricted cash	291	48
Net increase in cash, cash equivalents, and restricted cash	249,621	116,319
Cash, cash equivalents, and restricted cash, beginning of period	81,437	185,004
Cash, cash equivalents, and restricted cash, end of period	331,058	301,323
Supplemental disclosure of cash flow information
Cash paid for interest	674	556
Cash (refunded) paid for taxes, net	961	(152)
Supplemental disclosure of noncash investing and financing activities
Purchase of property and equipment, accrued but not paid	7,611	2,073
Obligation included in basis of acquired land	7,752	0
Lease incentive	3,193	0
Obligation included in basis of land acquired by the Developer	4,512	0
Equity awards withheld for tax liabilities, accrued but not paid	$ 132	$ 348

Organization and Description of

Organization and Description of Business	9 Months Ended
	Sep. 30, 2021
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 an international cloud-based, software-powered communications platform-as-a-service (“CPaaS”) provider that enables enterprises to create, scale and operate voice or messaging 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. On November 2, 2020, the Company acquired all of the A Ordinary Shares, B Ordinary Shares and C Ordinary Shares of Voice Topco Limited (“Voice Topco”) through a Share Purchase Agreement (the “Share Purchase Agreement” and such purchase, the “Share Purchase”). Voice Topco directly or indirectly held all of the issued and outstanding shares of Voxbone S.A., which (with its subsidiaries) was the operating subsidiary of Voice Topco (“Voxbone”). The transaction was valued at €446 million. As consideration for the Share Purchase, the Company (i) paid the selling stockholders approximately $400 million (or approximately €338 million based on prevailing exchange rates at the close of business on October 9, 2020) at the Closing and (ii) issued to the selling stockholders at the Closing shares of the Company’s Class A common stock, with an aggregate value of approximately €108 million (or approximately $128 million based on prevailing exchange rates at the close of business on October 9, 2020).

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
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 Securities and Exchange Commission (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 Company’s Annual Report on Form 10-K filed with the SEC on March 1, 2021. The condensed consolidated balance sheet as of December 31, 2020, included herein, was derived from the audited financial statements as of that date, but does not include all disclosures, including certain notes required by GAAP on an annual reporting basis. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the financial position, results of operations, comprehensive loss and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2021 or any future period. 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 condensed 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. These estimates in the condensed consolidated financial statements include, but are not limited to, allowance for doubtful accounts, reserve for expected credit losses, reserve for sales credits, recoverability of long lived and intangible assets, fair value of acquired intangible assets and goodwill, discount rates used in the valuation of right-of-use assets and lease liabilities, the fair value of the liability and equity components of the Company’s Convertible Notes (as defined herein), estimated period of benefit, valuation allowances on deferred tax assets, certain accrued expenses and contingencies, economic and demographic actuarial assumptions related to pension and other postretirement benefit costs and liabilities, estimated cash flows on asset retirement obligation. 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. Cash and Cash Equivalents The Company classifies all highly liquid investments with original stated maturities of three months or less from the date of purchase as cash equivalents. All highly liquid investments with original stated maturities of greater than three months from the date of purchase are classified as current marketable securities, with the exception of time deposits with maturities greater than ninety days which are classified as other investments. Cash deposits are primarily in financial institutions in the United States. However, cash for monthly operating costs of international operations are deposited in banks outside the United States. The Company has a policy of making investments only with commercial institutions that have at least an investment grade credit rating. The Company utilizes money market funds as an investment option and only invests in AAA rated funds. Restricted Cash Restricted cash consists primarily of the holdback amount and its accrued interest remaining to be paid to the selling stockholders of Voxbone, employee withholding tax liability and employee benefits contributions not yet remitted. The Company has classified this asset as a short-term asset in order to match the expected period of restriction. Accounts Receivable and Current Expected Credit Losses Accounts receivable are stated at realizable value, net of allowances, which includes an allowance for doubtful accounts and a reserve for expected credit losses. The allowance for doubtful accounts is based on management’s assessment of the collectability of its customer accounts. The Company regularly reviews the composition of the accounts receivable aging, historical bad debts, changes in payment patterns, customer creditworthiness, current economic trends, and reasonable and supportable forecasts about the future. Relevant risk characteristics include customer size and historical loss patterns. Management has evaluated the expected credit losses related to trade accounts receivable and determined that allowances of approximately $1,203 and $1,467 for uncollectible accounts and customer balances that are disputed were required as of December 31, 2020 and September 30, 2021, respectively. Refer to Note 5, “Financial Statement Components” to these condensed consolidated financial statements, for a rollforward of the components of the allowances as of December 31, 2020 and September 30, 2021. The Company includes unbilled receivables in its accounts receivable balance. Generally, these receivables represent earned revenue from services provided to customers, which will be billed in the next billing cycle. All amounts are considered collectible and billable. As of December 31, 2020 and September 30, 2021, unbilled receivables were $27,692 and $32,665, respectively. Concentration of Credit Risk Financial instruments that are exposed to concentration of credit risk consist primarily of cash and cash equivalents, other investments 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, 2020, one individual customer represented approximately 11% of the Company’s accounts receivable, net of allowance for doubtful accounts. As of September 30, 2021, one individual customer represented approximately 12% of the Company’s accounts receivable, net of allowance for doubtful accounts. For the three and nine months ended September 30, 2020 and 2021, no individual customer represented more than 10% of the Company’s revenue. Debt Issuance Costs The Company incurs debt issuance costs associated with obtaining and entering into credit agreements, including the issuances of convertible notes. These costs customarily include non-refundable structuring fees, commitment fees, up-front fees and syndication expenses. The Company has a policy of deferring and amortizing these costs based on the effective interest method over the term of the credit agreements. Recently Adopted Accounting Standards In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes , which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. ASU 2019-12 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The Company adopted this standard on January 1, 2021 on a prospective basis, which did not have a material impact on the Company’s financial statements. Recent Accounting Pronouncements Not Yet Adopted In May 2021, the FASB issued ASU 2021-04, Earnings Per Share (Topic 260), Debt —Modifications and Extinguishments (Subtopic 470-50), Compensation--Stock Compensation (Topic 718), and Derivatives and Hedging--Contracts in Entity's Own Equity (Subtopic 815-40) , which is intended to provide clarity surrounding the treatment for a modification or an exchange of a freestanding equity-classified written call option. The amendments also provide guidance for the recognition and measurement of earnings-per-share (“EPS”) for certain modifications or exchanges of freestanding equity-classified written call options for entities that present EPS. The amendments do not affect a holder’s accounting for freestanding call options. ASU 2021-04 is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company did not and does not expect to have any modification or exchanges of freestanding written call options classified in equity during the reporting period and therefore does not expect adoption will have a material impact on its financial statements. In August 2020, the FASB issued ASU 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity's Own Equity (Subtopic 815-40) , which is intended to address issues identified as a result of the complexity associated with applying GAAP for certain financial instruments with characteristics of liabilities and equity. For convertible instruments, ASU 2020-06 reduces the number of accounting models for convertible debt instruments and convertible preferred stock, and enhances information transparency by making targeted improvements to the disclosures for convertible instruments and EPS guidance on the basis of feedback from financial statement users. ASU 2020-06 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2021. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company will adopt the new guidance on January 1, 2022 using the modified retrospective approach resulting in adjustments in accumulated deficit and paid in capital. The Company will also record an increase in the convertible notes balance as a result of the reversal of the separation of the convertible debt between debt and equity. The adoption of this standard will decrease the amount of non-cash interest expense to be recognized in future periods as a result of eliminating the discount associated with the equity component. The number of diluted shares will increase as a result of transitioning from the treasury stock method to the as-if converted method for the calculation. The Company is currently quantifying the effect of adopting this new accounting guidance on its financial statements and earnings per share calculations.

Business Combination

Business Combination	9 Months Ended
	Sep. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Business Combination	3. Business Combination During the three months ended September 30, 2021, the Company made measurement period adjustments to reflect facts and circumstances in existence as of October 31, 2020, the effective date of the Share Purchase (the “Effective Date”). The adjustments primarily related to certain state and local tax liabilities that were not reasonably estimable at the Effective Date and consisted of a $1,609 increase to goodwill and $1,609 increase to accrued expenses and other current liabilities. The preliminary fair values of net assets acquired are substantially complete with the exception of certain working capital adjustments and goodwill. As the Company finalizes the fair value of assets acquired and liabilities assumed, additional purchase price adjustments may be recorded during the measurement period. The Company will reflect measurement period adjustments in the period in which the adjustments are recognized.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The carrying amounts of cash and cash equivalents, other investments, accounts receivable, accounts payable and accrued expenses approximate fair value as of December 31, 2020 and September 30, 2021 because of the relatively short duration of these instruments. 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, 2020 and September 30, 2021: Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 57,517 $ — $ — $ 57,517 Other investments: Time deposits 40,000 — — 40,000 Total financial assets $ 97,517 $ — $ — $ 97,517 Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 302,291 $ — $ — $ 302,291 Total financial assets $ 302,291 $ — $ — $ 302,291 As of September 30, 2021, the fair value of the 2026 and 2028 Convertible Notes, as further described in Note 9, “Debt”, was approximately $447,424 and $214,766, respectively. The fair value was determined based on the closing price for the Convertible Notes on the last trading day of the reporting period and is considered as Level 2 in the fair value hierarchy.

Financial Statement Components

Financial Statement Components	9 Months Ended
	Sep. 30, 2021
Financial Statement Components [Abstract]
Financial Statement Components	5. Financial Statement Components Accounts receivable, net of allowances consist of the following: As of December 31, As of September 30, 2020 2021 Trade accounts receivable $ 26,504 $ 42,987 Unbilled accounts receivable 27,692 32,665 Allowance for doubtful accounts and reserve for expected credit losses (1,203) (1,467) Other accounts receivable 2,250 976 Total accounts receivable, net $ 55,243 $ 75,161 Components of allowance for doubtful accounts and reserve for expected credit losses are as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Allowance for doubtful accounts: Balance, beginning of period $ (597) $ (1,364) $ (769) $ (1,203) Charged to bad debt expense (312) (169) (492) (475) Deductions (1) 20 54 372 182 Impact of foreign currency translation — 12 — 29 Balance, end of period $ (889) $ (1,467) $ (889) $ (1,467) ________________________ (1) Write off of uncollectible accounts after all collection efforts have been exhausted. Accrued expenses and other current liabilities consisted of the following: As of December 31, As of September 30, 2020 2021 Accrued expense $ 31,549 $ 39,444 Accrued compensation and benefits 19,534 17,341 Accrued sales, use, VAT and telecommunications related taxes 9,142 10,322 Current portion of finance lease 183 190 Obligation included in basis of acquired land — 7,752 Other accrued expenses 2,657 1,210 Total accrued expenses and other current liabilities $ 63,065 $ 76,259

Right-of-Use Asset and Lease Li

Right-of-Use Asset and Lease Liabilities	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Right-of-Use Asset and Lease Liabilities	6. Right-of-Use Asset and Lease Liabilities Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. The Company determines if an arrangement is a lease at inception. ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Operating lease expense attributable to lease payments is recognized on a straight-line basis over the lease term and is included in cost of sales and selling, general, and administrative expense on the Company’s condensed consolidated statements of operations. Finance leases result in the recognition of depreciation expense, which is recognized on a straight-line basis over the expected life of the leased asset, and interest expense, which is recognized following an effective interest rate method. Depreciation expense attributable to finance leases is included in cost of sales on the Company’s condensed consolidated statements of operations. The Company presents the operating leases in long-term assets and current and long-term liabilities in the accompanying condensed consolidated balance sheets. Finance leases are reported in property, plant and equipment, net, accrued expenses and other current liabilities, and other liabilities on the Company’s condensed consolidated balance sheets. The Company sub-leases approximately 17,073 square feet of office space to a related party, Relay, Inc. (f/k/a Republic Wireless, Inc.) (“Relay”). Future minimum sub-lease receipts required under the non-cancellable lease are as follows: As of September 30, 2021 2021 (remaining) $ 115 2022 249 $ 364 As of September 30, 2021, the Company had various leased properties in the United States and internationally, with remaining lease terms of nine months to 5.25 years, some of which include options to extend the leases for up to 5 years. None of the options to extend the leases are recognized in operating lease ROU assets or lease liabilities. The Company has one lease with an early-termination option, which it does not expect to exercise. The Company has one lease not yet commenced, with a lease term of 20 years and two options to extend the lease by a term of ten years each, up to twenty The components of lease expense recorded in general and administrative expenses in the condensed consolidated statement of operations were as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Operating lease cost $ 1,461 $ 1,699 $ 4,383 $ 5,002 Finance lease cost: Depreciation of assets — 60 — 165 Interest on lease liabilities — 5 — 14 Sublease income (1) (96) (96) (288) (288) Total net lease cost $ 1,365 $ 1,668 $ 4,095 $ 4,893 ________________________ (1) See Note 16, “Related Parties” to these condensed consolidated financial statements, for additional details on sublease income. During the three and nine months ended September 30, 2020, short-term operating lease expense was $0. During the three and nine months ended September 30, 2021, short-term operating lease expense was $372 and $1,098, respectively. Supplemental balance sheet information related to leases was as follows: As of December 31, As of September 30, Leases Classification 2020 2021 Assets: Operating lease assets Operating right-of-use asset, net (1) $ 19,491 $ 15,612 Finance lease assets Property, plant and equipment, net (2) 464 408 Total leased assets $ 19,955 $ 16,020 Liabilities: Current Operating Operating lease liability, current $ 5,515 $ 6,015 Finance Accrued expenses and other current liabilities 183 190 Non-current Operating Operating lease liability, net of current portion 17,202 12,525 Finance Other liabilities 282 224 Total lease liabilities $ 23,182 $ 18,954 ________________________ (1) Operating lease assets are recorded net of accumulated amortization of $9,083 and $13,298 as of December 31, 2020 and September 30, 2021, respectively. (2) Finance lease assets are recorded net of accumulated depreciation of $28 and $187 as of December 31, 2020 and September 30, 2021, respectively. Supplemental cash flow and other information related to leases was as follows: Nine months ended September 30, 2020 2021 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 3,944 $ 4,535 Financing cash flows from finance leases — 161 $ 3,944 $ 4,696 Weighted average remaining lease term (in years) Operating leases 3.65 3.14 Finance leases — 2.56 Weighted average discount rate Operating leases 4.99 % 4.77 % Finance leases — % 4.00 % Maturities of lease liabilities were as follows: As of September 30, 2021 Operating Leases Finance Leases 2021 (remaining) $ 1,362 $ 59 2022 6,991 182 2023 6,615 109 2024 2,665 74 2025 1,640 11 Thereafter 709 — Total lease payments 19,982 435 Less: imputed interest (1,442) (21) Total lease obligations 18,540 414 Less: current obligations (6,015) (190) Long-term lease obligations $ 12,525 $ 224 On June 4, 2021, the Company purchased approximately 40 acres of undeveloped land (the “Property”) in Raleigh, North Carolina, from the State of North Carolina (the “State”). The Company paid $30,017 for the land. Additionally, as consideration for the Property, the Company agreed to construct, at its expense, a parking lot and related improvements (the “Parking Improvements”) on land owned by the State adjacent to the Property. The estimated cost of construction of the Parking Improvements was $7,752. Subsequent to the purchase of the Property, the Company sold a portion of the Property constituting approximately 23.76 acres (the “Conveyed Parcel”) to USEF Edwards Mill Owner, LLC (the “Developer”) for $17,462. In addition, the Developer agreed to construct, at its expense, the Parking Improvements in connection with the Company’s purchase of the Property from the State. The Company retained approximately 17.06 acres of the Property, which was recorded at cost and is included in the Company’s condensed consolidated balance sheet as a component property, plant and equipment, net. The Company recorded a liability to construct the Parking Improvements, which is included as a component of accrued expenses and other current liabilities in the condensed consolidated balance sheet as of September 30, 2021. The Company recorded an asset for the Developer’s obligation to construct the Parking Improvements at the Developer's expense, which is included as a component of prepaid expenses and other current assets in the condensed consolidated balance sheet as of September 30, 2021. A lease incentive of $3,193 was recognized for the difference between the consideration received from the Developer for the Conveyed Parcel and the cost basis of the Conveyed Parcel and is included as a component of other liabilities on the condensed consolidated balance sheet. On October 1, 2021, the developer delivered the completed parking improvements and the State released the Company from its liability. On May 27, 2021, the Company entered into a Lease Agreement (the “Lease”) with the Developer for the Conveyed Parcel, together with improvements for office and related infrastructure to be constructed thereon, collectively constituting approximately 534,000 gross square feet (the “Project”). The lease became effective upon closing of the sale of the Conveyed Parcel to the Developer. When construction of the Project is completed, the Company intends to relocate its corporate headquarters to the Project. The lease term will commence upon substantial completion of the final building to be delivered, as evidenced by a certificate of occupancy issued by the City of Raleigh (the “Commencement Date”), and continue for a period of twenty

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	7. Property, Plant and Equipment Property, plant and equipment, net consisted of the following: As of December 31, As of September 30, 2020 2021 Furniture and fixtures $ 2,341 $ 2,179 Computer and office equipment 4,077 4,885 Telecommunications equipment 60,651 68,596 Leasehold improvements 6,285 6,260 Software 3,901 4,994 Internal-use software development 19,968 22,930 Automobile 502 605 Land — 16,394 Total cost 97,725 126,843 Less—accumulated depreciation (46,080) (58,576) Total property, plant and equipment, net $ 51,645 $ 68,267 The Company capitalized $348 and $1,846 of software development costs for the three and nine months ended September 30, 2020, respectively, and $808 and $3,212 for the three and nine months ended September 30, 2021, respectively. Amortization expense related to capitalized software development costs were $377 and $1,547 for the three and nine months ended September 30, 2020, respectively, and $459 and $1,404 for the three and nine months ended September 30, 2021, respectively. As of September 30, 2021, unamortized implementation costs related to cloud computing arrangements are $464, of which $140 are included in prepaid expenses and other current assets and $324 are included in other long-term assets. The Company leases automobiles under leases accounted for as finance leases with expiration dates ranging from December 31, 2021 to June 30, 2025. As of September 30, 2021, cost and accumulated depreciation of the assets under finance leases recorded by the Company were $595 and $187, respectively. The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Cost of revenue $ 2,284 $ 2,976 $ 6,958 $ 8,947 Research and development 197 296 441 829 Sales and marketing 30 32 90 90 General and administrative 646 1,165 2,048 3,117 Total depreciation expense $ 3,157 $ 4,469 $ 9,537 $ 12,983

Intangible Assets

Intangible Assets	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	8. Intangible Assets Intangible assets, net consisted of the following as of December 31, 2020: Gross Accumulated Net Carrying Amortization Dash acquisition and other intangibles: (Years) Customer relationships $ 10,396 $ (5,111) $ 5,285 20 Other, definite lived 3,933 (3,933) — 2 - 7 Licenses, indefinite lived 764 — 764 Indefinite Total Dash acquistion and other intangible assets 15,093 (9,044) 6,049 Voxbone acquistion: Customer relationships 156,559 (1,739) 154,820 15 Developed technology 88,664 (1,478) 87,186 10 Total Voxbone acquisition 245,223 (3,217) 242,006 Total intangible assets, net $ 260,316 $ (12,261) $ 248,055 Intangible assets, net consisted of the following as of September 30, 2021: Gross Accumulated Net Carrying Amortization Dash acquisition and other intangibles: (Years) Customer relationships $ 10,396 $ (5,501) $ 4,895 20 Other, definite lived 3,933 (3,933) — 2 - 7 Licenses, indefinite lived 764 — 764 Indefinite Total Dash acquisition and other intangible assets 15,093 (9,434) 5,659 Voxbone acquisition: Customer relationships 147,874 (9,037) 138,837 15 Developed technology 83,746 (7,676) 76,070 10 Total Voxbone acquisition 231,620 (16,713) 214,907 Total intangible assets, net $ 246,713 $ (26,147) $ 220,566 The Company recognized amortization expense as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Cost of revenue $ — $ 2,128 $ — $ 6,479 General and administrative 130 2,636 390 8,016 Total amortization expense $ 130 $ 4,764 $ 390 $ 14,495 The remaining weighted average amortization period for definite lived intangible assets is 12.2 years. Future estimated amortization expense for definite lived intangible assets is as follows: As of September 30, 2021 2021 (remaining) $ 4,688 2022 18,753 2023 18,753 2024 18,753 2025 18,753 Thereafter 140,102 $ 219,802

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	9. Debt Revolving Loan On May 25, 2021, the Company terminated the Credit and Security Agreement, dated as of November 4, 2016 as amended and restated as of March 1, 2019, among the Company, Key Bank National Association, and KeyBanc Capital Markets Inc. (the “Credit Agreement”). The agreement provided for a secured $25,000 revolving credit facility (the “Credit Facility”). As of December 31, 2020 and at the date of termination, no outstanding indebtedness existed under the Credit Facility and the Company was in compliance with all financial and non-financial covenants. As of December 31, 2020, unamortized debt issuance costs were $83, of which $74 were included in prepaid expenses and other current assets and $9 were included in other long-term assets. As of September 30, 2021, the outstanding debt issuance costs were $0. Convertible Senior Notes and Capped Call Transactions 2026 Convertible Notes On February 28, 2020, the Company issued $400,000 aggregate principal amount of 0.25% Convertible Notes due March 1, 2026 in a private placement to qualified institutional buyers pursuant to Rule 144A under the Securities Act (the “2026 Convertible Notes”). The interest on the 2026 Convertible Notes is payable semi-annually in arrears on March 1 and September 1 of each year, beginning on September 1, 2020. The 2026 Convertible Notes may bear special interest under specified circumstances relating to the Company's failure to comply with its reporting obligations under the indenture governing the 2026 Convertible Notes (the “2026 Indenture”) or if the 2026 Convertible Notes are not freely tradeable as required by the 2026 Indenture. The 2026 Convertible Notes will mature on March 1, 2026, unless earlier repurchased, redeemed by the Company, or converted pursuant to their terms. The total net proceeds from the 2026 Convertible Notes, after deducting initial purchaser discounts, costs related to the 2026 Capped Calls (as defined herein), and debt issuance costs, paid by the Company, were approximately $344,722. Each $1 principal amount of the 2026 Convertible Notes is initially convertible into 10.9857 shares of the Company's Class A common stock, par value $0.001 per share, which is equivalent to an initial conversion price of approximately $91.03 per share. The conversion rate is subject to adjustment upon the occurrence of certain specified events but will not be adjusted for any accrued and unpaid special interest. In addition, upon the occurrence of a make-whole fundamental change, as defined in the 2026 Indenture, the Company will, in certain circumstances, increase the conversion rate by a number of additional shares for a holder that elects to convert its 2026 Convertible Notes in connection with such make-whole fundamental change or during the relevant redemption period. The 2026 Convertible Notes will be redeemable in whole or in part at the Company's option on or after March 6, 2023, but before the fortieth (40 th ) scheduled trading day before the maturity date, at a cash redemption price equal to 100% of the principal amount of the 2026 Convertible Notes to be redeemed, plus accrued and unpaid interest, if any, if the last reported sale price of the Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading days ending on, and including, the trading day immediately before the date the redemption notices were sent; and the trading day immediately before such notices were sent. Prior to the close of business on the business day immediately preceding September 1, 2025, the 2026 Convertible Notes may be convertible at the option of the holders only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on June 30, 2020 (and only during such calendar quarter), if the last reported sale price per share of the Company's Class A common stock exceeds 130% of the conversion price for each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter; (2) during the five consecutive business days immediately after any 10 consecutive trading day period (such 10 consecutive trading day period, the “measurement period”) in which the trading price per $1 principal amount of 2026 Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price per share of the Company's Class A common stock on such trading day and the conversion rate on such trading day; (3) upon the occurrence of certain corporate events or distributions on its Class A common stock; and (4) if the Company calls such 2026 Convertible Notes for redemption. On or after September 1, 2025, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders of the 2026 Convertible Notes may, at their option, convert all or a portion of their 2026 Convertible Notes regardless of the foregoing conditions. Prior to and during the three and nine months ended September 30, 2021, the conditional conversion feature of the 2026 Convertible Notes was triggered as the last reported sale price of the Company's Class A common stock was more than or equal to 130% of the conversion price for at least 20 trading days (whether or not consecutive) in the period of 30 consecutive trading days ending on or after June 30, 2020 (the last trading day of the calendar quarter), and therefore the 2026 Convertible Notes were convertible, in whole or in part, at the option of the holders between July 1, 2020 through September 30, 2021. Whether the 2026 Convertible Notes will be convertible following such period will depend on the continued satisfaction of this condition or another conversion condition in the future. The Company continues to classify the 2026 Convertible Notes as a long-term liability in its condensed consolidated balance sheet as of September 30, 2021, based on contractual settlement provisions. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of Class A common stock, or a combination of cash and shares of Class A common stock, at the Company's election. It is the Company's current intent to settle the principal amount of the 2026 Convertible Notes with cash. No sinking fund is provided for the 2026 Convertible Notes. Upon the occurrence of a fundamental change (as defined in the 2026 Indenture) prior to the maturity date, holders may require the Company to repurchase all or a portion of the 2026 Convertible Notes for cash at a price equal to the principal amount of the 2026 Convertible Notes to be repurchased, plus any accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In accounting for the issuance of the 2026 Convertible Notes, the Company separated the 2026 Convertible Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar debt instrument that does not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was $125,160 and was determined by deducting the fair value of the liability component from the par value of the 2026 Convertible Notes. The difference represents the debt discount that is amortized to interest expense at an effective interest rate of 6.763% over the term of the 2026 Convertible Notes. The carrying amount of the equity component was $57,491 and is recorded in additional paid-in-capital. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. The excess of the principal amount of the liability component over its carrying amount, or the debt discount, is amortized to interest expense at an annual effective interest rate of 6.907% over the contractual terms of the 2026 Convertible Notes. In accounting for the transaction costs related to the 2026 Convertible Notes, the Company allocated the total amount incurred to the liability and equity components of the 2026 Convertible Notes based on the proportion of the proceeds allocated to the debt and equity components. Issuance costs attributable to the liability component were approximately $8,217, were recorded as an additional debt discount and are amortized to interest expense using the effective interest method over the contractual terms of the 2026 Convertible Notes. Issuance costs attributable to the equity component of $3,742 were netted with the equity component in stockholders’ equity. 2028 Convertible Notes On March 16, 2021, the Company issued $250,000 aggregate principal amount of 0.50% Convertible Notes due April 1, 2028 in a private placement to qualified institutional buyers pursuant to Rule 144A under the Securities Act (the “2028 Convertible Notes and, together with the 2026 Convertible Notes, the “Convertible Notes”). The interest on the 2028 Convertible Notes is payable semi-annually in arrears on April 1 and October 1 of each year, beginning on October 1, 2021. The 2028 Convertible Notes may bear special interest under specified circumstances relating to the Company's failure to comply with its reporting obligations under the indenture governing the 2028 Convertible Notes (the “2028 Indenture”) or if the 2028 Convertible Notes are not freely tradeable as required by the 2028 Indenture. The 2028 Convertible Notes will mature on April 1, 2028, unless earlier repurchased, redeemed by the Company, or converted pursuant to their terms. The total net proceeds from the 2028 Convertible Notes, after deducting initial purchaser discounts, costs related to the 2028 Capped Calls (as defined herein), and debt issuance costs, paid by the Company, were approximately $216,956. Each $1 principal amount of the 2028 Convertible Notes is initially convertible into 5.5781 shares of the Company's Class A common stock, par value $0.001 per share, which is equivalent to an initial conversion price of approximately $179.27 per share. The conversion rate is subject to adjustment upon the occurrence of certain specified events but will not be adjusted for any accrued and unpaid special interest. In addition, upon the occurrence of a make-whole fundamental change, as defined in the 2028 Indenture, the Company will, in certain circumstances, increase the conversion rate by a number of additional shares for a holder that elects to convert its 2028 Convertible Notes in connection with such make-whole fundamental change or during the relevant redemption period. The 2028 Convertible Notes will be redeemable in whole or in part at the Company's option on or after April 6, 2025, but before the fortieth (40 th ) scheduled trading day before the maturity date, at a cash redemption price equal to 100% of the principal amount of the 2028 Convertible Notes to be redeemed, plus accrued and unpaid interest, if any, if the last reported sale price of the Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading days ending on, and including, the trading day immediately before the date the redemption notices were sent; and the trading day immediately before such notices were sent. On or after April 6, 2025 until the close of business on the scheduled trading day immediately preceding the maturity date, the 2028 Convertible Notes may be convertible at the option of the holders only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on June 30, 2021 (and only during such calendar quarter), if the last reported sale price per share of the Company's Class A common stock exceeds 130% of the conversion price for each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter; (2) during the five consecutive business days immediately after any 10 consecutive trading day period (such 10 consecutive trading day period, the “measurement period”) in which the trading price per $1 principal amount of 2028 Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price per share of the Company's Class A common stock on such trading day and the conversion rate on such trading day; (3) upon the occurrence of certain corporate events or distributions on its Class A common stock; and (4) if the Company calls such 2028 Convertible Notes for redemption. On or after October 1, 2027, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders of the 2028 Convertible Notes may, at their option, convert all or a portion of their Convertible Notes regardless of the foregoing conditions. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of Class A common stock, or a combination of cash and shares of Class A common stock, at the Company's election. It is the Company's current intent to settle the principal amount of the 2028 Convertible Notes with cash. No sinking fund is provided for the 2028 Convertible Notes. Upon the occurrence of a fundamental change (as defined in the 2028 Indenture) prior to the maturity date, holders may require the Company to repurchase all or a portion of the 2028 Convertible Notes for cash at a price equal to the principal amount of the 2028 Convertible Notes to be repurchased, plus any accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In accounting for the issuance of the 2028 Convertible Notes, the Company separated the 2028 Convertible Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar debt instrument that does not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was $66,908 and was determined by deducting the fair value of the liability component from the par value of the 2028 Convertible Notes. The difference represents the debt discount that is amortized to interest expense at an effective interest rate of 5.125% over the term of the 2028 Convertible Notes. The carrying amount of the equity component was $39,389 and is recorded in additional paid-in-capital. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. The excess of the principal amount of the liability component over its carrying amount, or the debt discount, is amortized to interest expense at an annual effective interest rate of 4.959% over the contractual terms of the 2028 Convertible Notes. In accounting for the transaction costs related to the 2028 Convertible Notes, the Company allocated the total amount incurred to the liability and equity components of the 2028 Convertible Notes based on the proportion of the proceeds allocated to the debt and equity components. Issuance costs attributable to the liability component were approximately $5,525, were recorded as an additional debt discount and are amortized to interest expense using the effective interest method over the contractual terms of the 2028 Convertible Notes. Issuance costs attributable to the equity component of $2,019 were netted with the equity component in stockholders’ equity. The net carrying amount of the liability components of the 2026 and 2028 Convertible Notes were as follows: As of December 31, As of September 30, 2020 2021 2026 Convertible Notes: Principal $ 400,000 $ 400,000 Unamortized discount (110,546) (96,782) Unamortized debt issuance costs (7,258) (6,354) 2026 Convertible Notes net carrying amount 282,196 296,864 2028 Convertible Notes: Principal — 250,000 Unamortized discount — (62,542) Unamortized debt issuance costs — (5,167) 2028 Convertible Notes net carrying amount — 182,291 Total net carrying amount $ 282,196 $ 479,155 The net carrying amount of the equity components of the 2026 and 2028 Convertible Notes were as follows: As of December 31, As of September 30, 2020 2021 2026 Convertible Notes: Proceeds allocated to the conversion options (debt discount) $ 125,152 $ 125,152 Issuance costs (3,742) (3,742) 2026 Convertible Notes net carrying amount 121,410 121,410 2028 Convertible Notes: Proceeds allocated to the conversion options (debt discount) — 66,908 Issuance costs — (2,019) 2028 Convertible Notes net carrying amount — 64,889 Total net carrying amount $ 121,410 $ 186,299 The following table sets forth the interest expense recognized related to the 2026 and 2028 Convertible Notes: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 2026 Convertible Notes: Contractual interest expense $ 246 $ 250 $ 591 $ 750 Amortization of debt discount 4,292 4,664 10,183 13,761 Amortization of debt issuance costs 283 306 669 903 Total interest expense related to the 2026 Convertible Notes 4,821 5,220 11,443 15,414 2028 Convertible Notes: Contractual interest expense — 313 — 678 Amortization of debt discount — 2,029 — 4,366 Amortization of debt issuance costs — 168 — 362 Total interest expense related to the 2028 Convertible Notes — 2,510 — 5,406 Total interest expense $ 4,821 $ 7,730 $ 11,443 $ 20,820 In connection with the offering of the 2026 Convertible Notes and the 2028 Convertible Notes, the Company entered into privately negotiated capped call transactions with certain counterparties (the “2026 Capped Calls” and the “2028 Capped Calls,” respectively and, collectively, the “Capped Calls”). The 2026 Capped Calls and the 2028 Capped Calls each have an initial strike price of approximately $91.03 and $179.27 per share, respectively, subject to certain adjustments, which corresponds to the initial conversion price of the 2026 Convertible Notes and the 2028 Convertible Notes. The 2026 Capped Calls and the 2028 Capped Calls have initial cap prices of $137.40 and $260.76 per share subject to certain adjustments, respectively. The 2026 Capped Calls and the 2028 Capped Calls cover, subject to anti-dilution adjustments, approximately 4,394,276 and 1,394,525 shares of Class A common stock for the 2026 Convertible Notes and 2028 Convertible Notes, respectively. The Capped Calls are generally intended to reduce or offset the potential dilution to the Class A common stock upon any conversion of the 2026 Convertible Notes and 2028 Convertible Notes with such reduction or offset, as the case may be, subject to a cap based on the cap price. The Capped Calls expire on the earlier of (i) the last day on which any convertible securities remain outstanding and (ii) March 1, 2026 for the 2026 Capped Calls and April 1, 2028 for the 2028 Capped Calls, subject to earlier exercise. The Capped Calls are subject to either adjustment or termination upon the occurrence of specified extraordinary events affecting the Company, including a merger event, a tender offer, and a nationalization, insolvency or delisting involving the Company. In addition, the Capped Calls are subject to certain specified additional disruption events that may give rise to a termination of the Capped Calls, including changes in law, insolvency filings, and hedging disruptions. The Capped Call transactions are recorded in stockholders’ equity and are not accounted for as derivatives. The net cost of $43,320 and $25,500 incurred to purchase the 2026 Capped Calls and the 2028 Capped Calls, respectively, was recorded as a reduction to additional paid-in capital in the accompanying condensed consolidated balance sheets. The Convertible Notes are effectively subordinated to the Company’s future senior secured indebtedness, if any, to the extent of the value of the collateral securing that indebtedness. The Convertible notes are the senior, unsecured obligations of the Company and are equal in right of payment with the Company’s future senior unsecured indebtedness, if any, senior in right of payment to the Company’s existing and future indebtedness that is expressly subordinated to the Convertible Notes and the Convertible Notes will be structurally subordinated to all existing and future indebtedness and other liabilities, including trade payables, and preferred equity, if any, of the Company’s subsidiaries.

Segment and Geographic Informat

Segment and Geographic Information	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Segment and Geographic Information	10. 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 September 30, Nine months ended September 30, 2020 2021 2020 2021 CPaaS Revenue $ 73,762 $ 107,376 $ 199,959 $ 312,561 Cost of revenue 39,346 54,841 108,467 164,616 Gross profit $ 34,416 $ 52,535 $ 91,492 $ 147,945 Other Revenue $ 10,996 $ 23,262 $ 30,107 $ 52,214 Cost of revenue 6,181 17,554 15,428 35,166 Gross profit $ 4,815 $ 5,708 $ 14,679 $ 17,048 Consolidated Revenue $ 84,758 $ 130,638 $ 230,066 $ 364,775 Cost of revenue 45,527 72,395 123,895 199,782 Gross profit $ 39,231 $ 58,243 $ 106,171 $ 164,993 The Company’s long-lived assets were primarily held in the United States as of December 31, 2020 and September 30, 2021. As of December 31, 2020 and September 30, 2021, long-lived assets held outside of the United States were $11,249 and $10,156, respectively. 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 September 30, Nine months ended September 30, 2020 2021 2020 2021 CPaaS United States $ 71,809 $ 94,135 $ 194,414 $ 275,986 International 1,953 13,241 5,545 36,575 Total $ 73,762 $ 107,376 $ 199,959 $ 312,561 Other United States $ 10,584 $ 20,924 $ 29,127 $ 46,776 International 412 2,338 980 5,438 Total $ 10,996 $ 23,262 $ 30,107 $ 52,214

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	11. Stockholders’ Equity Preferred Stock As of December 31, 2020 and September 30, 2021, 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, 2020 and September 30, 2021, the Company had authorized 100,000,000 shares of Class A common stock, par value $0.001 per share, with one vote per share and 20,000,000 shares of Class B common stock, par value $0.001 per share, with ten votes per share. As of December 31, 2020, 22,413,004 and 2,496,125 shares of Class A common stock and Class B common stock, respectively, were issued and outstanding. As of September 30, 2021, 23,165,119 and 1,965,170 shares of Class A common stock and Class 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. Reserved Shares The Company had reserved shares of Class A common stock for issuance under stock-based award agreements as follows: As of December 31, As of September 30, 2020 2021 Stock options issued and outstanding 255,000 183,271 Nonvested restricted stock units issued and outstanding 450,614 369,614 Stock-based awards available for grant under the 2017 Plan 2,020,342 3,048,353 2,725,956 3,601,238

Stock Based Compensation

Stock Based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock Based Compensation	12. Stock Based Compensation 2010 Stock Option Plan As of July 26, 2010, the Company adopted the 2010 Equity Compensation Plan (the “2010 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, 2021, the shares available for grant under the 2017 Plan were automatically increased by 1,120,650 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 (“RSUs”) granted under the 2017 Plan are generally 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 RSUs to its non-employee members of the 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, 2020 255,000 $ 10.82 4.42 $ 36,426 Granted — — Exercised (70,923) 12.68 9,059 Forfeited or cancelled (806) 10.49 Outstanding as of September 30, 2021 183,271 $ 10.10 3.59 $ 14,694 Options vested and exercisable at September 30, 2021 178,878 $ 9.79 3.53 $ 14,398 Options vested and expected to vest as of September 30, 2021 183,032 $ 10.09 3.59 $ 14,678 Aggregate intrinsic value is computed based on the difference between the option exercise price and the fair value of the Company’s common stock as of September 30, 2021, based on the Company’s Class A common stock price as reported on the NASDAQ Global Select Market. No options were granted for the three and nine months ended September 30, 2020 and 2021. The total estimated grant date fair value of options vested was $193 and $322 for the three and nine months ended September 30, 2020, respectively, and $153 and $199 for the three and nine months ended September 30, 2021, respectively. As of September 30, 2021, total unrecognized compensation cost related to all non-vested stock options was $5, which will be amortized over a weighted-average period of 0.09 years. Restricted Stock Units The following summarizes the RSU activity for the periods presented: Number of awards outstanding Weighted-average grant date fair value (per share) Nonvested RSUs as of December 31, 2020 450,614 $ 51.58 Granted 146,989 146.80 Vested (173,695) 62.13 Forfeited or cancelled (54,294) 74.82 Nonvested RSUs as of September 30, 2021 369,614 $ 84.11 As of September 30, 2021, total unrecognized compensation cost related to non-vested RSUs was $25,509, which will be amortized over a weighted-average period of 2.86 years. Stock-Based Compensation Expense The Company recognized total stock-based compensation expense as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Cost of revenue $ 46 $ 52 $ 161 $ 190 Research and development 508 621 1,581 2,055 Sales and marketing 369 519 1,140 1,591 General and administrative 1,459 2,633 4,424 7,756 Total $ 2,382 $ 3,825 $ 7,306 $ 11,592

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Operating Leases The Company leases office space under operating lease agreements that expire over the next 5.25 years. See Note 6, “Right-of-Use Asset and Lease Liabilities” to the condensed consolidated financial statements, for additional details on the Company's operating lease commitments. 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 associated with the services received. The service agreement is non-cancellable and contains annual minimum commitments. On August 1, 2020, the Company amended the agreement to require annual minimum commitments of $600 and $300 in 2021 and 2022, respectively. In addition, as of September 30, 2021, the Company has $17,287 in other non-cancellable purchase obligations, consisting of primarily network equipment maintenance and software license contracts, of which $11,824 will be fulfilled within one year. On May 27, 2021, the Company entered into the Lease with the Developer for the Conveyed Parcel, together with the Project. The respective obligations of the Company and the Developer under the Lease were conditioned upon the Developer acquiring fee simple title to the Conveyed Parcel, which occurred on June 4, 2021. The Lease term will commence upon the Commencement Date and continue for the Initial Term. It is anticipated that the Commencement Date will occur in May 2023. If the Commencement Date does not occur within one hundred twenty twelve The Company has the option to renew the Initial Term for two ten-year periods. Base rent payments will begin on the Commencement Date. The initial base rent will increase by 1.85% on each anniversary of the Commencement Date. Total lease payments over the Initial Term are approximately $496,000. See Note 6, “Right-of-Use Asset and Lease Liabilities” to the condensed consolidated financial statements, for additional details on the Company's operating lease commitments. Legal Matters The Company is involved as a defendant in various litigation, including but not limited to 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.

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Employee Benefit Plans	14. Employee Benefit Plans The Company sponsors a U.S. defined contribution 401(k), which allows eligible U.S.-based employees to defer a portion of their compensation. The Company, at its discretion, may make matching contributions. With the acquisition of Voxbone S.A. on November 1, 2020, the Company assumed sponsorship for Voxbone S.A.’s U.S. defined contribution 401(k). In connection with that acquisition, the Company also assumed sponsorship for a non-U.S. defined contribution plan for which it pays fixed contributions into a separate entity. The Company has no legal or constructive obligations to pay further contributions if the fund does not hold sufficient assets to pay all employees the benefits relating to employee service in the current or prior periods. The contributions are recognized as employee benefit expense when they are due. The Company made matching contributions for the defined contribution plans of $474 and $1,583 for the three and nine months ended September 30, 2020, respectively, and $811 and $2,565 for the three and nine months ended September 30, 2021, respectively. In addition, as a result of the acquisition of Voxbone S.A., the Company assumed sponsorship for Voxbone S.A.’s non-U.S. defined benefit pension plans. The liability recognized in the other liabilities line item of the balance sheet in respect to these plans is the present value of the defined benefit obligation at the end of the reporting period less the fair value of the plan assets. The defined benefit obligation is calculated annually by an independent actuary using the Projected Unit Credit Method. The Company reports the service cost component of net periodic benefit cost in the same line item as other compensation costs arising from the services rendered by the employee and records the other components of net periodic benefit cost in other expense, net. Net periodic benefit costs for the non-U.S. defined benefit pension plan were $0 for the three and nine months ended September 30, 2020, and $105 and $323 for the three and nine months ended September 30, 2021, respectively. Pretax amounts for net periodic benefit cost and other amounts for the defined benefit pension plans consisted of the following components: Three months ended September 30, Nine months ended September 30, 2021 2021 Service cost $ 104 $ 318 Interest cost 5 16 Return on plan assets (4) (11) Net periodic pension cost 105 323 Total recognized in net periodic benefit cost $ 105 $ 323 Defined benefit cost: Expected long-term rate of return on plan assets 0.50 % 0.50 %

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	15. 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 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 was (0.4)% and (134.2)% for the three and nine months ended September 30, 2020, respectively, and (4.8)% and (1.3)% for the three and nine months ended September 30, 2021, respectively. The change in tax rate is primarily due to the valuation allowance recorded against U.S. deferred tax assets and the mix of earnings between various jurisdictions. The Company continues to maintain a valuation allowance for its U.S. federal and state net deferred tax assets. Judgment is required in determining whether deferred tax assets will be realized in full or in part. Management assesses the available positive and negative evidence on a jurisdictional basis to estimate if deferred tax assets will be recognized and when it is more likely than not that all or some deferred tax assets will not be realized, and a valuation allowance must be established. The Company’s effective tax rate for the three and nine months ended September 30, 2021 is lower than the U.S. federal statutory rate of 21.0% primarily due to the valuation allowance recorded against U.S. deferred tax assets.

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Parties	16. Related Parties The Company has certain involvement with Relay, Inc. (f/k/a Republic Wireless, Inc.) (“Relay”) via ongoing services arrangements, with these ongoing services arrangements creating a variable interest in Relay. The Company recorded a reduction of rent expense under the Facilities Sharing Agreement of $96 and $288 for the three and nine months ended September 30, 2020, respectively, and $96 and $288 for the three and nine months ended September 30, 2021, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations. No amounts were due to the Company under the Facilities Sharing Agreement as of December 31, 2020 and September 30, 2021. The Company provided telecommunication services to Relay under the Master Services Agreement of $541 and $1,657 for the three and nine months ended September 30, 2020, respectively, and $425 and $1,374 for the three and nine months ended September 30, 2021, respectively. The Company recognized such amounts as revenue in the accompanying condensed consolidated statements of operations. As of December 31, 2020 and September 30, 2021, the Company had a receivable of $170 and $142, respectively, under the Master Services Agreement. Bandwidth had collected on behalf of, and remitted withholding tax to, Relay of $747 and $1,295 for the three and nine months ended September 30, 2020, respectively, and $16 and $360 for the three and nine months ended September 30, 2021, respectively, for Relay employees that exercised Bandwidth stock options. As of December 31, 2020 and September 30, 2021, the Company had amounts payable to Relay of $0 and $16, respectively. The Company is compensated by Relay for services performed by the Company’s legal department based on costs incurred. The Company received net compensation of $16 and $63 for the three and nine months ended September 30, 2020, respectively, and $6 and $19 for the three and nine months ended September 30, 2021, respectively, which is included in general and administrative expenses in the condensed consolidated statements of operations. As of December 31, 2020 and September 30, 2021, the Company had a receivable of $2 under this agreement.

Basic and Diluted Loss per Comm

Basic and Diluted Loss per Common Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Basic and Diluted Loss per Common Share	17. Basic and Diluted Loss per Common Share Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. The Company is in a net loss position for the three and nine months ended September 30, 2020 and 2021 and therefore diluted shares equals basic shares. The components of basic and diluted loss per share are as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Earnings per share Net loss attributable to common stockholders $ (2,352) $ (6,944) $ (24,051) $ (19,188) Net loss per share, basic and diluted $ (0.10) $ (0.28) $ (1.01) $ (0.77) Weighted average number of common shares outstanding, basic and diluted 24,175,762 25,114,762 23,905,322 25,075,941 The following common share equivalents were excluded from the weighted average shares used to calculate net loss per common share because their effects would have been anti-dilutive: As of September 30, 2020 2021 Stock options issued and outstanding 269,108 183,271 Restricted stock units issued and outstanding 447,449 369,614 Convertible senior notes (1) 708,073 1,316,199 Total 1,424,630 1,869,084 ________________________ (1) As of September 30, 2020 and September 30, 2021, the Company used the treasury stock method to calculate the dilutive impact of the 2026 and 2028 Convertible Notes because at that time the Company expected to settle the principal amount of these notes in cash and any excess in shares of the Company's Class A common stock. As of September 30, 2020 and September 30, 2021, the conversion spread, calculated using the average market price of Class A common stock during the period consistent with the treasury stock method, had a dilutive impact for the 2026 Convertible Notes on diluted net income per share of Class A common stock when the average market price of the Company's Class A common stock for a given period exceeded the conversion price of $91.03 per share. As of September 30, 2021, the conversion spread for the 2028 Convertible Notes was anti-dilutive as the average market price of the Company's Class A common stock for a given period did not exceed the conversion price of $179.27 per share.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
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 Securities and Exchange Commission (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 Company’s Annual Report on Form 10-K filed with the SEC on March 1, 2021. The condensed consolidated balance sheet as of December 31, 2020, included herein, was derived from the audited financial statements as of that date, but does not include all disclosures, including certain notes required by GAAP on an annual reporting basis. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the financial position, results of operations, comprehensive loss and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2021 or any future period.
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 condensed 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. These estimates in the condensed consolidated financial statements include, but are not limited to, allowance for doubtful accounts, reserve for expected credit losses, reserve for sales credits, recoverability of long lived and intangible assets, fair value of acquired intangible assets and goodwill, discount rates used in the valuation of right-of-use assets and lease liabilities, the fair value of the liability and equity components of the Company’s Convertible Notes (as defined herein), estimated period of benefit, valuation allowances on deferred tax assets, certain accrued expenses and contingencies, economic and demographic actuarial assumptions related to pension and other postretirement benefit costs and liabilities, estimated cash flows on asset retirement obligation. 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.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents The Company classifies all highly liquid investments with original stated maturities of three months or less from the date of purchase as cash equivalents. All highly liquid investments with original stated maturities of greater than three months from the date of purchase are classified as current marketable securities, with the exception of time deposits with maturities greater than ninety days which are classified as other investments. Cash deposits are primarily in financial institutions in the United States. However, cash for monthly operating costs of international operations are deposited in banks outside the United States. The Company has a policy of making investments only with commercial institutions that have at least an investment grade credit rating. The Company utilizes money market funds as an investment option and only invests in AAA rated funds. Restricted Cash Restricted cash consists primarily of the holdback amount and its accrued interest remaining to be paid to the selling stockholders of Voxbone, employee withholding tax liability and employee benefits contributions not yet remitted. The Company has classified this asset as a short-term asset in order to match the expected period of restriction.
Accounts Receivable	Accounts Receivable and Current Expected Credit Losses Accounts receivable are stated at realizable value, net of allowances, which includes an allowance for doubtful accounts and a reserve for expected credit losses. The allowance for doubtful accounts is based on management’s assessment of the collectability of its customer accounts. The Company regularly reviews the composition of the accounts receivable aging, historical bad debts, changes in payment patterns, customer creditworthiness, current economic trends, and reasonable and supportable forecasts about the future. Relevant risk characteristics include customer size and historical loss patterns. Management has evaluated the expected credit losses related to trade accounts receivable and determined that allowances of approximately $1,203 and $1,467 for uncollectible accounts and customer balances that are disputed were required as of December 31, 2020 and September 30, 2021, respectively. Refer to Note 5, “Financial Statement Components” to these condensed consolidated financial statements, for a rollforward of the components of the allowances as of December 31, 2020 and September 30, 2021. The Company includes unbilled receivables in its accounts receivable balance. Generally, these receivables represent earned revenue from services provided to customers, which will be billed in the next billing cycle. All
Current Expected Credit Losses	Accounts Receivable and Current Expected Credit Losses Accounts receivable are stated at realizable value, net of allowances, which includes an allowance for doubtful accounts and a reserve for expected credit losses. The allowance for doubtful accounts is based on management’s assessment of the collectability of its customer accounts. The Company regularly reviews the composition of the accounts receivable aging, historical bad debts, changes in payment patterns, customer creditworthiness, current economic trends, and reasonable and supportable forecasts about the future. Relevant risk characteristics include customer size and historical loss patterns. Management has evaluated the expected credit losses related to trade accounts receivable and determined that allowances of approximately $1,203 and $1,467 for uncollectible accounts and customer balances that are disputed were required as of December 31, 2020 and September 30, 2021, respectively. Refer to Note 5, “Financial Statement Components” to these condensed consolidated financial statements, for a rollforward of the components of the allowances as of December 31, 2020 and September 30, 2021. The Company includes unbilled receivables in its accounts receivable balance. Generally, these receivables represent earned revenue from services provided to customers, which will be billed in the next billing cycle. All
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, other investments 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.
Debt Issuance Costs	Debt Issuance CostsThe Company incurs debt issuance costs associated with obtaining and entering into credit agreements, including the issuances of convertible notes. These costs customarily include non-refundable structuring fees, commitment fees, up-front fees and syndication expenses. The Company has a policy of deferring and amortizing these costs based on the effective interest method over the term of the credit agreements.
Recently Adopted Accounting Standards and Recent Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Standards In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes , which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. ASU 2019-12 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The Company adopted this standard on January 1, 2021 on a prospective basis, which did not have a material impact on the Company’s financial statements. Recent Accounting Pronouncements Not Yet Adopted In May 2021, the FASB issued ASU 2021-04, Earnings Per Share (Topic 260), Debt —Modifications and Extinguishments (Subtopic 470-50), Compensation--Stock Compensation (Topic 718), and Derivatives and Hedging--Contracts in Entity's Own Equity (Subtopic 815-40) , which is intended to provide clarity surrounding the treatment for a modification or an exchange of a freestanding equity-classified written call option. The amendments also provide guidance for the recognition and measurement of earnings-per-share (“EPS”) for certain modifications or exchanges of freestanding equity-classified written call options for entities that present EPS. The amendments do not affect a holder’s accounting for freestanding call options. ASU 2021-04 is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company did not and does not expect to have any modification or exchanges of freestanding written call options classified in equity during the reporting period and therefore does not expect adoption will have a material impact on its financial statements. In August 2020, the FASB issued ASU 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity's Own Equity (Subtopic 815-40) , which is intended to address issues identified as a result of the complexity associated with applying GAAP for certain financial instruments with characteristics of liabilities and equity. For convertible instruments, ASU 2020-06 reduces the number of accounting models for convertible debt instruments and convertible preferred stock, and enhances information transparency by making targeted improvements to the disclosures for convertible instruments and EPS guidance on the basis of feedback from financial statement users. ASU 2020-06 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2021. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company will adopt the new guidance on January 1, 2022 using the modified retrospective approach resulting in adjustments in accumulated deficit and paid in capital. The Company will also record an increase in the convertible notes balance as a result of the reversal of the separation of the convertible debt between debt and equity. The adoption of this standard will decrease the amount of non-cash interest expense to be recognized in future periods as a result of eliminating the discount associated with the equity component. The number of diluted shares will increase as a result of transitioning from the treasury stock method to the as-if converted method for the calculation. The Company is currently quantifying the effect of adopting this new accounting guidance on its financial statements and earnings per share calculations.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
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, 2020 and September 30, 2021: Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 57,517 $ — $ — $ 57,517 Other investments: Time deposits 40,000 — — 40,000 Total financial assets $ 97,517 $ — $ — $ 97,517 Fair value measurements on a recurring basis Level 1 Level 2 Level 3 Total Financial assets: Cash and cash equivalents: Money market account $ 302,291 $ — $ — $ 302,291 Total financial assets $ 302,291 $ — $ — $ 302,291

Financial Statement Components

Financial Statement Components (Tables)	9 Months Ended
	Sep. 30, 2021
Financial Statement Components [Abstract]
Schedule of Accounts Receivable, net, and Allowance for Doubtful Accounts	Accounts receivable, net of allowances consist of the following: As of December 31, As of September 30, 2020 2021 Trade accounts receivable $ 26,504 $ 42,987 Unbilled accounts receivable 27,692 32,665 Allowance for doubtful accounts and reserve for expected credit losses (1,203) (1,467) Other accounts receivable 2,250 976 Total accounts receivable, net $ 55,243 $ 75,161 Components of allowance for doubtful accounts and reserve for expected credit losses are as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Allowance for doubtful accounts: Balance, beginning of period $ (597) $ (1,364) $ (769) $ (1,203) Charged to bad debt expense (312) (169) (492) (475) Deductions (1) 20 54 372 182 Impact of foreign currency translation — 12 — 29 Balance, end of period $ (889) $ (1,467) $ (889) $ (1,467) ________________________ (1) Write off of uncollectible accounts after all collection efforts have been exhausted.
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: As of December 31, As of September 30, 2020 2021 Accrued expense $ 31,549 $ 39,444 Accrued compensation and benefits 19,534 17,341 Accrued sales, use, VAT and telecommunications related taxes 9,142 10,322 Current portion of finance lease 183 190 Obligation included in basis of acquired land — 7,752 Other accrued expenses 2,657 1,210 Total accrued expenses and other current liabilities $ 63,065 $ 76,259

Right-of-Use Asset and Lease _2

Right-of-Use Asset and Lease Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
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 September 30, 2021 2021 (remaining) $ 115 2022 249 $ 364
Components of Lease Expense	The components of lease expense recorded in general and administrative expenses in the condensed consolidated statement of operations were as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Operating lease cost $ 1,461 $ 1,699 $ 4,383 $ 5,002 Finance lease cost: Depreciation of assets — 60 — 165 Interest on lease liabilities — 5 — 14 Sublease income (1) (96) (96) (288) (288) Total net lease cost $ 1,365 $ 1,668 $ 4,095 $ 4,893 ________________________ (1) See Note 16, “Related Parties” to these condensed consolidated financial statements, for additional details on sublease income. Supplemental cash flow and other information related to leases was as follows: Nine months ended September 30, 2020 2021 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 3,944 $ 4,535 Financing cash flows from finance leases — 161 $ 3,944 $ 4,696 Weighted average remaining lease term (in years) Operating leases 3.65 3.14 Finance leases — 2.56 Weighted average discount rate Operating leases 4.99 % 4.77 % Finance leases — % 4.00 %
Supplemental Balance Sheet Lease Information	Supplemental balance sheet information related to leases was as follows: As of December 31, As of September 30, Leases Classification 2020 2021 Assets: Operating lease assets Operating right-of-use asset, net (1) $ 19,491 $ 15,612 Finance lease assets Property, plant and equipment, net (2) 464 408 Total leased assets $ 19,955 $ 16,020 Liabilities: Current Operating Operating lease liability, current $ 5,515 $ 6,015 Finance Accrued expenses and other current liabilities 183 190 Non-current Operating Operating lease liability, net of current portion 17,202 12,525 Finance Other liabilities 282 224 Total lease liabilities $ 23,182 $ 18,954 ________________________ (1) Operating lease assets are recorded net of accumulated amortization of $9,083 and $13,298 as of December 31, 2020 and September 30, 2021, respectively. (2) Finance lease assets are recorded net of accumulated depreciation of $28 and $187 as of December 31, 2020 and September 30, 2021, respectively.
Schedule of Maturities of Operating Lease Liabilities	Maturities of lease liabilities were as follows: As of September 30, 2021 Operating Leases Finance Leases 2021 (remaining) $ 1,362 $ 59 2022 6,991 182 2023 6,615 109 2024 2,665 74 2025 1,640 11 Thereafter 709 — Total lease payments 19,982 435 Less: imputed interest (1,442) (21) Total lease obligations 18,540 414 Less: current obligations (6,015) (190) Long-term lease obligations $ 12,525 $ 224
Schedule of Maturities of Finance Lease Liabilities	Maturities of lease liabilities were as follows: As of September 30, 2021 Operating Leases Finance Leases 2021 (remaining) $ 1,362 $ 59 2022 6,991 182 2023 6,615 109 2024 2,665 74 2025 1,640 11 Thereafter 709 — Total lease payments 19,982 435 Less: imputed interest (1,442) (21) Total lease obligations 18,540 414 Less: current obligations (6,015) (190) Long-term lease obligations $ 12,525 $ 224

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment, Net	Property, plant and equipment, net consisted of the following: As of December 31, As of September 30, 2020 2021 Furniture and fixtures $ 2,341 $ 2,179 Computer and office equipment 4,077 4,885 Telecommunications equipment 60,651 68,596 Leasehold improvements 6,285 6,260 Software 3,901 4,994 Internal-use software development 19,968 22,930 Automobile 502 605 Land — 16,394 Total cost 97,725 126,843 Less—accumulated depreciation (46,080) (58,576) Total property, plant and equipment, net $ 51,645 $ 68,267
Schedule of Depreciation Expense	The Company recognized depreciation expense, which includes amortization of capitalized software development costs, as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Cost of revenue $ 2,284 $ 2,976 $ 6,958 $ 8,947 Research and development 197 296 441 829 Sales and marketing 30 32 90 90 General and administrative 646 1,165 2,048 3,117 Total depreciation expense $ 3,157 $ 4,469 $ 9,537 $ 12,983

Intangible Assets (Tables)

Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite Lived Intangible Assets	Intangible assets, net consisted of the following as of December 31, 2020: Gross Accumulated Net Carrying Amortization Dash acquisition and other intangibles: (Years) Customer relationships $ 10,396 $ (5,111) $ 5,285 20 Other, definite lived 3,933 (3,933) — 2 - 7 Licenses, indefinite lived 764 — 764 Indefinite Total Dash acquistion and other intangible assets 15,093 (9,044) 6,049 Voxbone acquistion: Customer relationships 156,559 (1,739) 154,820 15 Developed technology 88,664 (1,478) 87,186 10 Total Voxbone acquisition 245,223 (3,217) 242,006 Total intangible assets, net $ 260,316 $ (12,261) $ 248,055 Intangible assets, net consisted of the following as of September 30, 2021: Gross Accumulated Net Carrying Amortization Dash acquisition and other intangibles: (Years) Customer relationships $ 10,396 $ (5,501) $ 4,895 20 Other, definite lived 3,933 (3,933) — 2 - 7 Licenses, indefinite lived 764 — 764 Indefinite Total Dash acquisition and other intangible assets 15,093 (9,434) 5,659 Voxbone acquisition: Customer relationships 147,874 (9,037) 138,837 15 Developed technology 83,746 (7,676) 76,070 10 Total Voxbone acquisition 231,620 (16,713) 214,907 Total intangible assets, net $ 246,713 $ (26,147) $ 220,566
Schedule of Infinite Lived Intangible Assets	Intangible assets, net consisted of the following as of December 31, 2020: Gross Accumulated Net Carrying Amortization Dash acquisition and other intangibles: (Years) Customer relationships $ 10,396 $ (5,111) $ 5,285 20 Other, definite lived 3,933 (3,933) — 2 - 7 Licenses, indefinite lived 764 — 764 Indefinite Total Dash acquistion and other intangible assets 15,093 (9,044) 6,049 Voxbone acquistion: Customer relationships 156,559 (1,739) 154,820 15 Developed technology 88,664 (1,478) 87,186 10 Total Voxbone acquisition 245,223 (3,217) 242,006 Total intangible assets, net $ 260,316 $ (12,261) $ 248,055 Intangible assets, net consisted of the following as of September 30, 2021: Gross Accumulated Net Carrying Amortization Dash acquisition and other intangibles: (Years) Customer relationships $ 10,396 $ (5,501) $ 4,895 20 Other, definite lived 3,933 (3,933) — 2 - 7 Licenses, indefinite lived 764 — 764 Indefinite Total Dash acquisition and other intangible assets 15,093 (9,434) 5,659 Voxbone acquisition: Customer relationships 147,874 (9,037) 138,837 15 Developed technology 83,746 (7,676) 76,070 10 Total Voxbone acquisition 231,620 (16,713) 214,907 Total intangible assets, net $ 246,713 $ (26,147) $ 220,566
Schedule of Amortization Expense	The Company recognized amortization expense as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Cost of revenue $ — $ 2,128 $ — $ 6,479 General and administrative 130 2,636 390 8,016 Total amortization expense $ 130 $ 4,764 $ 390 $ 14,495
Schedule of Future Estimated Amortization Expense	Future estimated amortization expense for definite lived intangible assets is as follows: As of September 30, 2021 2021 (remaining) $ 4,688 2022 18,753 2023 18,753 2024 18,753 2025 18,753 Thereafter 140,102 $ 219,802

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Net Carrying Amount of Liability and Equity Component of Notes	The net carrying amount of the liability components of the 2026 and 2028 Convertible Notes were as follows: As of December 31, As of September 30, 2020 2021 2026 Convertible Notes: Principal $ 400,000 $ 400,000 Unamortized discount (110,546) (96,782) Unamortized debt issuance costs (7,258) (6,354) 2026 Convertible Notes net carrying amount 282,196 296,864 2028 Convertible Notes: Principal — 250,000 Unamortized discount — (62,542) Unamortized debt issuance costs — (5,167) 2028 Convertible Notes net carrying amount — 182,291 Total net carrying amount $ 282,196 $ 479,155 The net carrying amount of the equity components of the 2026 and 2028 Convertible Notes were as follows: As of December 31, As of September 30, 2020 2021 2026 Convertible Notes: Proceeds allocated to the conversion options (debt discount) $ 125,152 $ 125,152 Issuance costs (3,742) (3,742) 2026 Convertible Notes net carrying amount 121,410 121,410 2028 Convertible Notes: Proceeds allocated to the conversion options (debt discount) — 66,908 Issuance costs — (2,019) 2028 Convertible Notes net carrying amount — 64,889 Total net carrying amount $ 121,410 $ 186,299
Interest Income and Interest Expense Disclosure	The following table sets forth the interest expense recognized related to the 2026 and 2028 Convertible Notes: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 2026 Convertible Notes: Contractual interest expense $ 246 $ 250 $ 591 $ 750 Amortization of debt discount 4,292 4,664 10,183 13,761 Amortization of debt issuance costs 283 306 669 903 Total interest expense related to the 2026 Convertible Notes 4,821 5,220 11,443 15,414 2028 Convertible Notes: Contractual interest expense — 313 — 678 Amortization of debt discount — 2,029 — 4,366 Amortization of debt issuance costs — 168 — 362 Total interest expense related to the 2028 Convertible Notes — 2,510 — 5,406 Total interest expense $ 4,821 $ 7,730 $ 11,443 $ 20,820

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Schedule of Segment Information	Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 CPaaS Revenue $ 73,762 $ 107,376 $ 199,959 $ 312,561 Cost of revenue 39,346 54,841 108,467 164,616 Gross profit $ 34,416 $ 52,535 $ 91,492 $ 147,945 Other Revenue $ 10,996 $ 23,262 $ 30,107 $ 52,214 Cost of revenue 6,181 17,554 15,428 35,166 Gross profit $ 4,815 $ 5,708 $ 14,679 $ 17,048 Consolidated Revenue $ 84,758 $ 130,638 $ 230,066 $ 364,775 Cost of revenue 45,527 72,395 123,895 199,782 Gross profit $ 39,231 $ 58,243 $ 106,171 $ 164,993
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 September 30, Nine months ended September 30, 2020 2021 2020 2021 CPaaS United States $ 71,809 $ 94,135 $ 194,414 $ 275,986 International 1,953 13,241 5,545 36,575 Total $ 73,762 $ 107,376 $ 199,959 $ 312,561 Other United States $ 10,584 $ 20,924 $ 29,127 $ 46,776 International 412 2,338 980 5,438 Total $ 10,996 $ 23,262 $ 30,107 $ 52,214

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Schedule of Reserved Shares of Common Stock for Issuance	The Company had reserved shares of Class A common stock for issuance under stock-based award agreements as follows: As of December 31, As of September 30, 2020 2021 Stock options issued and outstanding 255,000 183,271 Nonvested restricted stock units issued and outstanding 450,614 369,614 Stock-based awards available for grant under the 2017 Plan 2,020,342 3,048,353 2,725,956 3,601,238

Stock Based Compensation (Table

Stock Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [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, 2020 255,000 $ 10.82 4.42 $ 36,426 Granted — — Exercised (70,923) 12.68 9,059 Forfeited or cancelled (806) 10.49 Outstanding as of September 30, 2021 183,271 $ 10.10 3.59 $ 14,694 Options vested and exercisable at September 30, 2021 178,878 $ 9.79 3.53 $ 14,398 Options vested and expected to vest as of September 30, 2021 183,032 $ 10.09 3.59 $ 14,678
Summary of Restricted Stock Unit Activity	The following summarizes the RSU activity for the periods presented: Number of awards outstanding Weighted-average grant date fair value (per share) Nonvested RSUs as of December 31, 2020 450,614 $ 51.58 Granted 146,989 146.80 Vested (173,695) 62.13 Forfeited or cancelled (54,294) 74.82 Nonvested RSUs as of September 30, 2021 369,614 $ 84.11
Schedule of Stock-Based Compensation Expense	The Company recognized total stock-based compensation expense as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Cost of revenue $ 46 $ 52 $ 161 $ 190 Research and development 508 621 1,581 2,055 Sales and marketing 369 519 1,140 1,591 General and administrative 1,459 2,633 4,424 7,756 Total $ 2,382 $ 3,825 $ 7,306 $ 11,592

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Summary of Accumulated Benefit Obligation in Excess of Plan Assets	Pretax amounts for net periodic benefit cost and other amounts for the defined benefit pension plans consisted of the following components: Three months ended September 30, Nine months ended September 30, 2021 2021 Service cost $ 104 $ 318 Interest cost 5 16 Return on plan assets (4) (11) Net periodic pension cost 105 323 Total recognized in net periodic benefit cost $ 105 $ 323 Defined benefit cost: Expected long-term rate of return on plan assets 0.50 % 0.50 %

Basic and Diluted Loss per Co_2

Basic and Diluted Loss per Common Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The components of basic and diluted loss per share are as follows: Three months ended September 30, Nine months ended September 30, 2020 2021 2020 2021 Earnings per share Net loss attributable to common stockholders $ (2,352) $ (6,944) $ (24,051) $ (19,188) Net loss per share, basic and diluted $ (0.10) $ (0.28) $ (1.01) $ (0.77) Weighted average number of common shares outstanding, basic and diluted 24,175,762 25,114,762 23,905,322 25,075,941
Schedule of Anti-dilutive Common Shares Excluded from Calculation of Net Loss	The following common share equivalents were excluded from the weighted average shares used to calculate net loss per common share because their effects would have been anti-dilutive: As of September 30, 2020 2021 Stock options issued and outstanding 269,108 183,271 Restricted stock units issued and outstanding 447,449 369,614 Convertible senior notes (1) 708,073 1,316,199 Total 1,424,630 1,869,084 ________________________ (1) As of September 30, 2020 and September 30, 2021, the Company used the treasury stock method to calculate the dilutive impact of the 2026 and 2028 Convertible Notes because at that time the Company expected to settle the principal amount of these notes in cash and any excess in shares of the Company's Class A common stock. As of September 30, 2020 and September 30, 2021, the conversion spread, calculated using the average market price of Class A common stock during the period consistent with the treasury stock method, had a dilutive impact for the 2026 Convertible Notes on diluted net income per share of Class A common stock when the average market price of the Company's Class A common stock for a given period exceeded the conversion price of $91.03 per share. As of September 30, 2021, the conversion spread for the 2028 Convertible Notes was anti-dilutive as the average market price of the Company's Class A common stock for a given period did not exceed the conversion price of $179.27 per share.

Organization and Description _2

Organization and Description of Business (Details) $ / shares in Units, € in Millions, $ in Millions	Nov. 02, 2020EUR (€)	Nov. 02, 2020USD ($)	Sep. 30, 2021segment	Mar. 16, 2021$ / shares	Feb. 28, 2020$ / shares
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments | segment			2
Number of reportable segments | segment			2
0.25% Convertible senior notes due 2026 | Convertible notes
Business Acquisition [Line Items]
Conversion price (in usd per share) | $ / shares					$ 91.03
0.50% Convertible senior notes due 2028 | Convertible notes
Business Acquisition [Line Items]
Conversion price (in usd per share) | $ / shares				$ 179.27
Voxbone S.A
Business Acquisition [Line Items]
Total purchase consideration | €	€ 446
Fair value of cash paid	338	$ 400
Voxbone S.A | Common stock
Business Acquisition [Line Items]
Fair value of Bandwidth common stock issued	€ 108	$ 128

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Cash and Cash Equivalents and Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Allowance for doubtful accounts	$ 1,467	$ 1,203
Unbilled accounts receivable	$ 32,665	$ 27,692

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Accounts Receivable and Current Expected Credit Losses and Concentration of Credit Risk and Deferred Revenue and Customer Deposits (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Customer One | Customer | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk percentage	12.00%	11.00%

Business Combination (Details)

Business Combination (Details) $ in Thousands	3 Months Ended
	Sep. 30, 2021USD ($)
Business Combination and Asset Acquisition [Abstract]
Goodwill measurement period adjustments	$ 1,609
Increase in accrued expenses and other current liabilities	$ 1,609

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Details) - Fair value measurements on a recurring basis - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 302,291	$ 57,517
Time deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other investments		40,000
Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	302,291	97,517
Level 1 | Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	302,291	57,517
Level 1 | Time deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other investments		40,000
Level 1 | Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	302,291	97,517
Level 2 | Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Level 2 | Time deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other investments		0
Level 2 | Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0	0
Level 3 | Money market account
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Level 3 | Time deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other investments		0
Level 3 | Financial assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 0	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - Convertible notes $ in Thousands	Sep. 30, 2021USD ($)
0.25% Convertible senior notes due 2026
Debt Instrument [Line Items]
Fair value	$ 447,424
0.50% Convertible senior notes due 2028
Debt Instrument [Line Items]
Fair value	$ 214,766

Financial Statement Component_2

Financial Statement Components - Accounts Receivable, Net of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial Statement Components [Abstract]
Trade accounts receivable	$ 42,987	$ 26,504
Unbilled accounts receivable	32,665	27,692
Allowance for doubtful accounts and reserve for expected credit losses	(1,467)	(1,203)
Other accounts receivable	976	2,250
Total accounts receivable, net	$ 75,161	$ 55,243

Financial Statement Component_3

Financial Statement Components - Allowance For Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period	$ (1,364)	$ (597)	$ (1,203)	$ (769)
Charged to bad debt expense	(169)	(312)	(475)	(492)
Deductions	54	20	182	372
Impact of foreign currency translation	12	0	29	0
Balance, end of period	$ (1,467)	$ (889)	$ (1,467)	$ (889)

Financial Statement Component_4

Financial Statement Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial Statement Components [Abstract]
Accrued expense	$ 39,444	$ 31,549
Accrued compensation and benefits	17,341	19,534
Accrued sales, use, VAT and telecommunications related taxes	10,322	9,142
Current portion of finance lease	190	183
Obligation included in basis of acquired land	7,752	0
Other accrued expenses	1,210	2,657
Total accrued expenses and other current liabilities	$ 76,259	$ 63,065

Right-of-Use Asset and Lease _3

Right-of-Use Asset and Lease Liabilities - Additional Information (Details) $ in Thousands	Jun. 05, 2021USD ($)a	Jun. 04, 2021USD ($)a	May 27, 2021USD ($)ft²lease	Sep. 30, 2021USD ($)leaseft²	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)leaseft²	Sep. 30, 2020USD ($)
Lessee, Lease, Description [Line Items]
Option to extend, term				5 years		5 years
Number of leases with early-termination option | lease				1		1
Short-term operating lease expense				$ 372	$ 0	$ 1,098	$ 0
Consideration for the proposed Land purchase						30,017	0
Proceeds from sale of land						$ 17,462	$ 0
Lease not yet commenced
Lessee, Lease, Description [Line Items]
Number of lease not yet commenced | lease						1
Lease term				20 years		20 years
Number of option to extend | lease			2			2
Term of option to extend			10 years			10 years
Total available extensions						20 years
Office space (in square foot) | ft²			534,000
Term of lease			20 years
Market rental rate			100.00%
Escrow to fund			$ 3,000
Lease not yet commenced | Developer
Lessee, Lease, Description [Line Items]
Security deposit			$ 2,500
Property
Lessee, Lease, Description [Line Items]
Land (acres) | a	17.06	40
Consideration for the proposed Land purchase		$ 30,017
Estimated cost of construction		$ 7,752
Lease incentive	$ 3,193
Property | Developer
Lessee, Lease, Description [Line Items]
Area of land sold | a	23.76
Proceeds from sale of land	$ 17,462
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term				9 months		9 months
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term				5 years 3 months		5 years 3 months
Relay, Inc
Lessee, Lease, Description [Line Items]
Sublease | ft²				17,073		17,073

Right-of-Use Asset and Lease _4

Right-of-Use Asset and Lease Liabilities - Future Minimum Sub-lease Receipts (Details) $ in Thousands	Sep. 30, 2021USD ($)
Leases [Abstract]
2021 (remaining)	$ 115
2022	249
Total	$ 364

Right-of-Use Asset and Lease _5

Right-of-Use Asset and Lease Liabilities - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease cost	$ 1,699	$ 1,461	$ 5,002	$ 4,383
Depreciation of assets	60	0	165	0
Interest on lease liabilities	5	0	14	0
Sublease income	(96)	(96)	(288)	(288)
Total net lease cost	$ 1,668	$ 1,365	$ 4,893	$ 4,095

Right-of-Use Asset and Lease _6

Right-of-Use Asset and Lease Liabilities - Supplemental Balance Sheet Lease Information (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Operating lease assets	$ 15,612	$ 19,491
Finance lease assets	408	464
Total leased assets	16,020	19,955
Current
Operating	6,015	5,515
Finance	190	183
Non-current
Long-term lease obligations	12,525	17,202
Long-term lease obligations	224	282
Total lease obligations	$ 18,954	$ 23,182
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other current liabilities	Accrued expenses and other current liabilities
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other liabilities	Other liabilities
Accumulated amortization	$ 13,298	$ 9,083
Accumulated depreciation of assets under finance leases	$ 187	$ 28

Right-of-Use Asset and Lease _7

Right-of-Use Asset and Lease Liabilities - Supplemental Cash Flow and Other Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 4,535	$ 3,944
Financing cash flows from finance leases	161	0
Lease liabilities	$ 4,696	$ 3,944
Weighted average remaining lease term (in years)
Operating leases	3 years 1 month 20 days	3 years 7 months 24 days
Finance leases	2 years 6 months 21 days		0 years
Weighted average discount rate
Operating leases	4.77%	4.99%
Finance leases	4.00%	0.00%

Right-of-Use Asset and Lease _8

Right-of-Use Asset and Lease Liabilities - Schedule of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Operating Leases
2021 (remaining)	$ 1,362
2022	6,991
2023	6,615
2024	2,665
2025	1,640
Thereafter	709
Total lease payments	19,982
Less: imputed interest	(1,442)
Total lease obligations	18,540
Less: current obligations	(6,015)	$ (5,515)
Long-term lease obligations	12,525	17,202
Finance Leases
2021 (remaining)	59
2022	182
2023	109
2024	74
2025	11
Thereafter	0
Total lease payments	435
Less: imputed interest	(21)
Total lease obligations	414
Less: current obligations	(190)	(183)
Long-term lease obligations	$ 224	$ 282

Property, Plant and Equipment -

Property, Plant and Equipment - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total cost	$ 126,843	$ 97,725
Less—accumulated depreciation	(58,576)	(46,080)
Property, plant and equipment, net	68,267	51,645
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total cost	2,179	2,341
Computer and office equipment
Property, Plant and Equipment [Line Items]
Total cost	4,885	4,077
Telecommunications equipment
Property, Plant and Equipment [Line Items]
Total cost	68,596	60,651
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total cost	6,260	6,285
Software
Property, Plant and Equipment [Line Items]
Total cost	4,994	3,901
Internal-use software development
Property, Plant and Equipment [Line Items]
Total cost	22,930	19,968
Automobile
Property, Plant and Equipment [Line Items]
Total cost	605	502
Land
Property, Plant and Equipment [Line Items]
Total cost	$ 16,394	$ 0

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Capitalized software development costs, additions	$ 808	$ 348	$ 3,212	$ 1,846
Amortization of capitalized software development costs	459	$ 377	1,404	$ 1,547
Capitalized implementation costs related to cloud computing arrangements	464		464
Cost of assets under finance leases	595		595
Accumulated depreciation of assets under finance leases	187		187		$ 28
Prepaid expenses and other current assets
Property, Plant and Equipment [Line Items]
Capitalized implementation costs related to cloud computing arrangements	140		140
Other long-term assets
Property, Plant and Equipment [Line Items]
Capitalized implementation costs related to cloud computing arrangements	$ 324		$ 324

Property, Plant and Equipment_3

Property, Plant and Equipment - Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Depreciation Expense [Line Items]
Total depreciation expense	$ 4,469	$ 3,157	$ 12,983	$ 9,537
Cost of revenue
Depreciation Expense [Line Items]
Total depreciation expense	2,976	2,284	8,947	6,958
Research and development
Depreciation Expense [Line Items]
Total depreciation expense	296	197	829	441
Sales and marketing
Depreciation Expense [Line Items]
Total depreciation expense	32	30	90	90
General and administrative
Depreciation Expense [Line Items]
Total depreciation expense	$ 1,165	$ 646	$ 3,117	$ 2,048

Intangible Assets - Summary of

Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Dash acquisition and other intangibles:
Accumulated Amortization	$ (26,147)	$ (12,261)
Finite-lived intangible assets, net	219,802
Gross Amount	246,713	260,316
Net Carrying Value	220,566	248,055
Dash
Dash acquisition and other intangibles:
Accumulated Amortization	(9,434)	(9,044)
Gross Amount	15,093	15,093
Net Carrying Value	5,659	6,049
Dash | Licenses
Dash acquisition and other intangibles:
Licenses, indefinite lived	764	764
Dash | Customer relationships
Dash acquisition and other intangibles:
Finite-lived intangible assets, gross	10,396	10,396
Accumulated Amortization	(5,501)	(5,111)
Finite-lived intangible assets, net	$ 4,895	$ 5,285
Amortization Period	20 years	20 years
Dash | Other, definite lived
Dash acquisition and other intangibles:
Finite-lived intangible assets, gross	$ 3,933	$ 3,933
Accumulated Amortization	(3,933)	(3,933)
Finite-lived intangible assets, net	$ 0	$ 0
Dash | Other, definite lived | Minimum
Dash acquisition and other intangibles:
Amortization Period	2 years	2 years
Dash | Other, definite lived | Maximum
Dash acquisition and other intangibles:
Amortization Period	7 years	7 years
Voxbone S.A
Dash acquisition and other intangibles:
Accumulated Amortization	$ (16,713)	$ (3,217)
Gross Amount	231,620	245,223
Net Carrying Value	214,907	242,006
Voxbone S.A | Customer relationships
Dash acquisition and other intangibles:
Finite-lived intangible assets, gross	147,874	156,559
Accumulated Amortization	(9,037)	(1,739)
Finite-lived intangible assets, net	$ 138,837	$ 154,820
Amortization Period	15 years	15 years
Voxbone S.A | Developed technology
Dash acquisition and other intangibles:
Finite-lived intangible assets, gross	$ 83,746	$ 88,664
Accumulated Amortization	(7,676)	(1,478)
Finite-lived intangible assets, net	$ 76,070	$ 87,186
Amortization Period	10 years	10 years

Intangible Assets - Additional

Intangible Assets - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Weighted average useful life	12 years 2 months 12 days

Intangible Assets - Amortizatio

Intangible Assets - Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Goodwill [Line Items]
Total amortization expense	$ 4,764	$ 130	$ 14,495	$ 390
Cost of revenue
Goodwill [Line Items]
Total amortization expense	2,128	0	6,479	0
General and administrative
Goodwill [Line Items]
Total amortization expense	$ 2,636	$ 130	$ 8,016	$ 390

Intangible Assets - Future Esti

Intangible Assets - Future Estimated Amortization Expense (Details) $ in Thousands	Sep. 30, 2021USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2021 (remaining)	$ 4,688
2022	18,753
2023	18,753
2024	18,753
2025	18,753
Thereafter	140,102
Finite-lived intangible assets, net	$ 219,802

Debt - Revolving Loan (Details)

Debt - Revolving Loan (Details) - USD ($)	Sep. 30, 2021	May 25, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Outstanding unamortized loan fees			$ 83,000
Prepaid expenses and other current assets
Debt Instrument [Line Items]
Outstanding unamortized loan fees	$ 0		74,000
Other long-term assets
Debt Instrument [Line Items]
Outstanding unamortized loan fees			9,000
Credit Facility
Debt Instrument [Line Items]
Borrowing capacity		$ 25,000,000
Long-term debt			$ 0

Debt - 2026 Convertible Notes (

Debt - 2026 Convertible Notes (Details)	Feb. 28, 2020USD ($)day$ / shares	Sep. 30, 2021USD ($)$ / shares	Dec. 31, 2020USD ($)$ / shares
Debt Instrument [Line Items]
Total net proceeds	$ 344,722,000
Class A voting common stock
Debt Instrument [Line Items]
Common stock, par value (in usd per share) | $ / shares		$ 0.001	$ 0.001
2026 Convertible Notes
Debt Instrument [Line Items]
Cash redemption price, percent	100.00%
2026 Convertible Notes | Class A voting common stock
Debt Instrument [Line Items]
Common stock, par value (in usd per share) | $ / shares	$ 0.001
2026 Convertible Notes | Convertible notes
Debt Instrument [Line Items]
Principal	$ 400,000,000	$ 400,000,000	$ 400,000,000
Stated rate	0.25%
Conversion price (in usd per share) | $ / shares	$ 91.03
Conversion option	$ 125,160,000
Effective interest rate	6.763%
Carrying amount of equity component	$ 57,491,000
Annual effective interest rate	6.907%
Issuance costs attributable to the liability component	$ 8,217,000
Issuance costs	$ 3,742,000	$ 3,742,000	$ 3,742,000
2026 Convertible Notes | Convertible notes | Conversion option 2
Debt Instrument [Line Items]
Trading days | day	5,000
Consecutive trading days | day	10,000
2026 Convertible Notes | Convertible notes | Class A voting common stock
Debt Instrument [Line Items]
Conversion ratio	10.9857
2026 Convertible Notes | Convertible notes | Class A voting common stock | Conversion option 1
Debt Instrument [Line Items]
Stock price trigger percent	130.00%
Trading days | day	20
Consecutive trading days | day	30
2026 Convertible Notes | Convertible notes | Class A voting common stock | Conversion option 2
Debt Instrument [Line Items]
Stock price trigger percent	98.00%

Debt - 2028 Convertible Notes (

Debt - 2028 Convertible Notes (Details)	Mar. 16, 2021USD ($)day$ / shares	Feb. 28, 2020USD ($)	Sep. 30, 2021USD ($)$ / shares	Dec. 31, 2020USD ($)$ / shares
Debt Instrument [Line Items]
Total net proceeds		$ 344,722,000
Class A voting common stock
Debt Instrument [Line Items]
Common stock, par value (in usd per share) | $ / shares			$ 0.001	$ 0.001
2028 Convertible Notes | Class A voting common stock
Debt Instrument [Line Items]
Common stock, par value (in usd per share) | $ / shares	$ 0.001
2028 Convertible Notes | Convertible notes
Debt Instrument [Line Items]
Principal	$ 250,000,000		$ 250,000,000	$ 0
Stated rate	0.50%
Total net proceeds	$ 216,956,000
Conversion price (in usd per share) | $ / shares	$ 179.27
Cash redemption price, percent	100.00%
Conversion option	$ 66,908,000
Effective interest rate	5.125%
Carrying amount of equity component	$ 39,389,000
Annual effective interest rate	4.959%
Issuance costs attributable to the liability component	$ 5,525,000
Issuance costs	$ 2,019,000		$ 2,019,000	$ 0
2028 Convertible Notes | Convertible notes | Class A voting common stock
Debt Instrument [Line Items]
Conversion ratio	5.5781
2028 Convertible Notes | Convertible notes | Conversion option 1
Debt Instrument [Line Items]
Trading days | day	20
Consecutive trading days | day	30
2028 Convertible Notes | Convertible notes | Conversion option 1 | Class A voting common stock
Debt Instrument [Line Items]
Stock price trigger percent	130.00%
2028 Convertible Notes | Convertible notes | Conversion option 2
Debt Instrument [Line Items]
Trading days | day	5,000
Consecutive trading days | day	10,000
2028 Convertible Notes | Convertible notes | Conversion option 2 | Class A voting common stock
Debt Instrument [Line Items]
Stock price trigger percent	98.00%

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - Convertible notes - USD ($)	Sep. 30, 2021	Mar. 16, 2021	Dec. 31, 2020	Feb. 28, 2020
Debt Instrument [Line Items]
Total net carrying amount	$ 479,155,000		$ 282,196,000
Total net carrying amount	186,299,000		121,410,000
2026 Convertible Notes
Debt Instrument [Line Items]
Principal	400,000,000		400,000,000	$ 400,000,000
Unamortized discount	(96,782,000)		(110,546,000)
Unamortized debt issuance costs	(6,354,000)		(7,258,000)
Total net carrying amount	296,864,000		282,196,000
Proceeds allocated to the conversion options (debt discount)	125,152,000		125,152,000
Issuance costs	(3,742,000)		(3,742,000)	$ (3,742,000)
Total net carrying amount	121,410,000		121,410,000
2028 Convertible Notes
Debt Instrument [Line Items]
Principal	250,000,000	$ 250,000,000	0
Unamortized discount	(62,542,000)		0
Unamortized debt issuance costs	(5,167,000)		0
Total net carrying amount	182,291,000		0
Proceeds allocated to the conversion options (debt discount)	66,908,000		0
Issuance costs	(2,019,000)	$ (2,019,000)	0
Total net carrying amount	$ 64,889,000		$ 0

Debt - Interest Income and Inte

Debt - Interest Income and Interest Expense Disclosure (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Total interest expense	$ 7,730	$ 4,821	$ 20,820	$ 11,443
2026 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	250	246	750	591
Amortization of debt discount	4,664	4,292	13,761	10,183
Amortization of debt issuance costs	306	283	903	669
Total interest expense	5,220	4,821	15,414	11,443
2028 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	313	0	678	0
Amortization of debt discount	2,029	0	4,366	0
Amortization of debt issuance costs	168	0	362	0
Total interest expense	$ 2,510	$ 0	$ 5,406	$ 0

Debt - Convertible Senior Notes

Debt - Convertible Senior Notes and Capped Call Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 16, 2021	Feb. 28, 2020
Debt Instrument [Line Items]
Net cost of capped call purchase	$ 25,500	$ 43,320
Class A voting common stock
Debt Instrument [Line Items]
Capped call shares (in shares)	1,394,525	4,394,276
Convertible notes | 0.25% Convertible senior notes due 2026
Debt Instrument [Line Items]
Initial conversion strike price (in usd per share)		$ 91.03
Initial cap price (in usd per share)		$ 137.40
Convertible notes | 0.50% Convertible senior notes due 2028
Debt Instrument [Line Items]
Initial conversion strike price (in usd per share)	$ 179.27
Initial cap price (in usd per share)	$ 260.76

Segment and Geographic Inform_3

Segment and Geographic Information - Reconciliation of Segment Profit (Loss) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)segment	Sep. 30, 2020USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			2
Segment Reporting Information [Line Items]
Revenue	$ 130,638	$ 84,758	$ 364,775	$ 230,066
Cost of revenue	72,395	45,527	199,782	123,895
Gross profit	58,243	39,231	164,993	106,171
CPaaS
Segment Reporting Information [Line Items]
Revenue	107,376	73,762	312,561	199,959
Cost of revenue	54,841	39,346	164,616	108,467
Gross profit	52,535	34,416	147,945	91,492
Other
Segment Reporting Information [Line Items]
Revenue	23,262	10,996	52,214	30,107
Cost of revenue	17,554	6,181	35,166	15,428
Gross profit	$ 5,708	$ 4,815	$ 17,048	$ 14,679

Segment and Geographic Inform_4

Segment and Geographic Information - Reconciliation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Assets	$ 1,100,926		$ 1,100,926		$ 890,608
Revenue	130,638	$ 84,758	364,775	$ 230,066
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Assets	10,156		10,156		$ 11,249
CPaaS
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	107,376	73,762	312,561	199,959
CPaaS | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	94,135	71,809	275,986	194,414
CPaaS | International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	13,241	1,953	36,575	5,545
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	23,262	10,996	52,214	30,107
Other | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	20,924	10,584	46,776	29,127
Other | International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 2,338	$ 412	$ 5,438	$ 980

Stockholders' Equity - Preferre

Stockholders' Equity - Preferred Stock (Details) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
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

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock (Details)	Sep. 30, 2021vote$ / sharesshares	Dec. 31, 2020vote$ / sharesshares
Class A voting common stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, par value (in usd per share) | $ / shares	$ 0.001	$ 0.001
Common stock voting rights | vote	1	1
Common stock, shares issued (in shares)	23,165,119	22,413,004
Common stock, shares outstanding (in shares)	23,165,119	22,413,004
Class B voting common stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, par value (in usd per share) | $ / shares	$ 0.001	$ 0.001
Common stock voting rights | vote	10	10
Common stock, shares issued (in shares)	1,965,170	2,496,125
Common stock, shares outstanding (in shares)	1,965,170	2,496,125

Stockholders' Equity - Reserved

Stockholders' Equity - Reserved Shares of Common Stock for Issuance (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	3,601,238	2,725,956
Stock options issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	183,271	255,000
Nonvested restricted stock units issued and outstanding
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	369,614	450,614
Stock-based awards available for grant under the 2017 Plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	3,048,353	2,020,342

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Details) - USD ($) $ in Thousands	Jan. 01, 2021	Jan. 01, 2018	Nov. 09, 2017	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)				3,601,238		3,601,238		2,725,956
Estimated grant date fair value of options vested				$ 153	$ 193	$ 199	$ 322
Unrecognized cost for stock based compensation				$ 5		$ 5
Stock options issued and outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options, granted (in shares)				0	0	0	0
Unrecognized cost for stock based compensation, period for recognition (in years)						1 month 2 days
Restricted stock units issued and outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)				369,614		369,614		450,614
Unrecognized cost for stock based compensation, period for recognition (in years)						2 years 10 months 9 days
Unrecognized compensation cost related to non-vested RSUs				$ 25,509		$ 25,509
2010 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares)				0		0
2017 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)	1,120,650
2017 Plan | Stock options issued and outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			4 years
Contractual life (in years)			10 years
2017 Plan | Restricted stock units issued and outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period			4 years
2017 Plan | Restricted stock units issued and outstanding | Non-employee Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
2017 Plan | Restricted stock units issued and outstanding | Executives
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			4 years
2017 Plan | Restricted stock units issued and outstanding | Executives | Year one vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			50.00%
2017 Plan | Restricted stock units issued and outstanding | Executives | First quarter vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%
2017 Plan | Restricted stock units issued and outstanding | Executives | Second quarter vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%
2017 Plan | Restricted stock units issued and outstanding | Executives | Third quarter vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%
2017 Plan | Restricted stock units issued and outstanding | Executives | First quarter vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			12.50%
2017 Plan | Restricted stock units issued and outstanding | Executives | Year two, three and four vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			50.00%

Stock Based Compensation - Stoc

Stock Based Compensation - Stock Option Activity (Details) - Stock options issued and outstanding - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Number of options outstanding
Number of options outstanding, beginning balance (in shares)			255,000
Number of options, granted (in shares)	0	0	0	0
Number of options exercised (in shares)			(70,923)
Number of options, forfeited or cancelled (in shares)			(806)
Number of options outstanding, ending balance (in shares)	183,271		183,271		255,000
Options vested and exercisable (in shares)	178,878		178,878
Options vested and expected to vest (in shares)	183,032		183,032
Weighted- average exercise price (per share)
Weighted-average exercise price, beginning balance (in usd per share)			$ 10.82
Weighted-average exercise price, granted (in usd per share)			0
Weighted-average exercise price, exercised (in usd per share)			12.68
Weighted-average exercise price, forfeited or cancelled (in usd per share)			10.49
Weighted-average exercise price, ending balance (in usd per share)	$ 10.10		10.10		$ 10.82
Weighted-average exercise price, options vested and exercisable (in usd per share)	9.79		9.79
Weighted average exercise price, options vested and expected to vest (in usd per share)	$ 10.09		$ 10.09
Weighted- average remaining contract life (in years)
Weighted-average remaining contract life, options outstanding (in years)			3 years 7 months 2 days		4 years 5 months 1 day
Weighted-average remaining contract life, options vested and exercisable (in years)			3 years 6 months 10 days
Weighted average remaining contract life, options vested and expected to vest			3 years 7 months 2 days
Aggregate intrinsic value  (in thousands)
Aggregate intrinsic value, options outstanding	$ 14,694		$ 14,694		$ 36,426
Aggregate intrinsic value, options exercised			9,059
Aggregate intrinsic value, options vested and exercisable	14,398		14,398
Aggregate intrinsic value, options vested and expected to vest	$ 14,678		$ 14,678

Stock Based Compensation - Rest

Stock Based Compensation - Restricted Stock Unit Activity (Details) - Restricted stock units issued and outstanding	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of awards outstanding
Number of nonvested RSUs outstanding, beginning balance (in shares) | shares	450,614
Number of nonvested RSUs, granted (in shares) | shares	146,989
Number of nonvested RSUs, vested (in shares) | shares	(173,695)
Number of nonvested RSUs, forfeited or cancelled (in shares) | shares	(54,294)
Number of nonvested RSUs outstanding, ending balance (in shares) | shares	369,614
Weighted-average grant date fair value (per share)
Weighted-average grant date fair value, beginning balance (in usd per share) | $ / shares	$ 51.58
Weighted average grant-date fair value of nonvested RSUs, granted (in usd per share) | $ / shares	146.80
Weighted-average grant date fair value of nonvested RSUs, vested (in usd per share) | $ / shares	62.13
Weighted-average grant date fair value of nonvested restricted RSUs, forfeited or cancelled (in usd per share) | $ / shares	74.82
Weighted-average grant date fair value, ending balance (in usd per share) | $ / shares	$ 84.11

Stock Based Compensation - St_2

Stock Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,825	$ 2,382	$ 11,592	$ 7,306
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	52	46	190	161
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	621	508	2,055	1,581
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	519	369	1,591	1,140
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,633	$ 1,459	$ 7,756	$ 4,424

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	May 27, 2021USD ($)lease	Sep. 30, 2021USD ($)lease	Aug. 01, 2020USD ($)
Lessee, Lease, Description [Line Items]
Annual minimum commitment, year one			$ 600
Annual minimum commitment, year two			$ 300
Non-cancellable purchase obligation		$ 17,287
Non-cancellable purchase obligation, fulfilled within a year		11,824
Lease payments of initial term		$ 19,982
Project
Lessee, Lease, Description [Line Items]
Commencement date, rent abatement period	120 days
Commencement delivered period	12 months
Number of option to extend | lease	2	2
Term of option to extend	10 years	10 years
Base rent percentage	1.85%
Lease payments of initial term	$ 496,000
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term		5 years 3 months

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Matching contributions	$ 811,000	$ 474,000	$ 2,565,000	$ 1,583,000
Non-U.S. | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost	$ 105,000	$ 0	$ 323,000	$ 0

Employee Benefit Plans - Summar

Employee Benefit Plans - Summary of Net Periodic Cost of Pension and Postretirement Benefit Plans (Details) - Pension Plan - Non-U.S. - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 104,000		$ 318,000
Interest cost	5,000		16,000
Return on plan assets	(4,000)		(11,000)
Net periodic pension cost	105,000	$ 0	323,000	$ 0
Total recognized in net periodic benefit cost	$ 105,000		$ 323,000
Expected long-term rate of return on plan assets	0.50%		0.50%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Effective tax rate	(4.80%)	(0.40%)	(1.30%)	(134.20%)

Related Parties (Details)

Related Parties (Details) - Affiliated Entity - Relay - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Amount collected on behalf	$ 16,000	$ 747,000	$ 360,000	$ 1,295,000
Payable	0		0		$ 16,000
Facilities Sharing Agreement
Related Party Transaction [Line Items]
Reduction of rent expense	96,000	96,000	288,000	288,000
Due from related parties	0		0		0
Master Services Agreement
Related Party Transaction [Line Items]
Revenue from related parties	425,000	541,000	1,374,000	1,657,000
Accounts receivable, related parties	142,000		142,000		170,000
Legal services
Related Party Transaction [Line Items]
Revenue from related parties	6,000	$ 16,000	19,000	$ 63,000
Accounts receivable, related parties	$ 2,000		$ 2,000		$ 2,000

Basic and Diluted Loss per Co_3

Basic and Diluted Loss per Common Share - Components of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (6,944)	$ (2,352)	$ (19,188)	$ (24,051)
Net loss per share, basic (in usd per share)	$ (0.28)	$ (0.10)	$ (0.77)	$ (1.01)
Net loss per share, diluted (in usd per share)	$ (0.28)	$ (0.10)	$ (0.77)	$ (1.01)
Weighted average number of common shares outstanding, basic (in shares)	25,114,762	24,175,762	25,075,941	23,905,322
Weighted average number of common shares outstanding, diluted (in shares)	25,114,762	24,175,762	25,075,941	23,905,322

Basic and Diluted Loss per Co_4

Basic and Diluted Loss per Common Share - Schedule of Antidilutive Common Share Equivalents Excluded from Earnings Per Share (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Mar. 16, 2021	Feb. 28, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	1,869,084	1,424,630
0.25% Convertible senior notes due 2026 | Convertible notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price (in usd per share)				$ 91.03
0.50% Convertible senior notes due 2028 | Convertible notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price (in usd per share)			$ 179.27
Stock options issued and outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	183,271	269,108
Restricted stock units issued and outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	369,614	447,449
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	1,316,199	708,073