Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES:
Net loss	$ (107,594)	$ (96,071)	$ (25,032)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense	65,946	44,105	14,841
Depreciation and amortization	22,826	16,366	14,188
Loss on disposal	5,147	0	0
Amortization of tenant allowance	0	(516)	(326)
Amortization of purchased intangibles and finance leases	3,552	2,932	2,813
Amortization of debt issuance costs	1,340	956	0
Accretion of debt discount on convertible senior notes	11,564	7,605	0
Change in fair value of contingent consideration	(263)	(328)	0
Provision for doubtful accounts, net	3,211	2,159	1,788
Deferred income taxes	579	(1,207)	(309)
Changes in operating assets and liabilities:
Accounts receivable	6,371	(43,757)	(9,662)
Prepaid expenses and other current assets	23	(4,712)	(12,993)
Contract acquisition costs noncurrent	(6,463)	(13,718)	(1,635)
Other assets	(37)	(30)	(107)
Accounts payable	(733)	3,808	2,199
Accrued expenses and other current liabilities	22,931	(10,882)	(205)
Deferred revenue	(3,118)	33,953	19,005
Decrease in net operating lease asset and liability	8,276	388	0
Deferred tax liability	0	0	0
Other liabilities	47	(209)	214
Net cash provided by (used in) operating activities	33,605	(59,158)	4,779
INVESTING ACTIVITIES:
Purchases of property and equipment, including capitalized software	(41,641)	(47,582)	(21,938)
Payments for acquisitions and intangible assets, net of cash acquired	(1,835)	(924)	(7,286)
Cash held as collateral	0	0	1,451
Net cash used in investing activities	(43,476)	(48,506)	(27,773)
FINANCING ACTIVITIES:
Principal payments for financing leases	(1,154)	0	0
Repurchase of common stock	0	(903)	(1,345)
Proceeds from issuance of common stock in connection with the exercise of options and ESPP	25,355	21,060	35,271
Proceeds from issuance of convertible senior notes	517,500	230,000	0
Payment of issuance costs in connection with convertible senior notes	(11,800)	(8,635)	0
Payment related to contingent consideration	0	(487)	0
Purchase of capped call option	(46,058)	(23,184)	0
Net cash provided by financing activities	483,843	217,851	33,926
EFFECT OF FOREIGN EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	3,657	(113)	(598)
CHANGE IN CASH AND CASH EQUIVALENTS	477,629	110,074	10,334
CASH AND CASH EQUIVALENTS - Beginning of the year	176,523	66,449	56,115
CASH AND CASH EQUIVALENTS - End of the year	654,152	176,523	66,449
SUPPLEMENTAL DISCLOSURE OF OTHER CASH FLOW INFORMATION:
Cash paid for income taxes	4,651	3,304	5,144
Cash paid for interest	1,931	848	0
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchase of property and equipment recorded in accounts payable	1,638	1,198	190
Leasehold improvements funded by landlord	0	0	1,551
Right of use assets obtained in exchange for operating lease liabilities	0	21,588	0
Right of use assets obtained in exchange for finance lease liabilities	10,818	0	0
Issuance of shares of common stock as earn-out payment in connection with AdvantageTec Inc.	$ 293
Issuance of shares of common stock as earn-out payment in connection with AdvantageTec Inc. (in shares)	11,508
Issuance of shares of common stock to settle cash awards	$ 24,657	0	0
Issuance of shares of common stock to settle cash awards (in shares)	991,905
Conversable Dec 13 2019
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Issuance of shares of common stock in connection with acquisition	$ 0	$ 1,000	0
Issuance of shares of common stock in connection with acquisition (in shares)		38,462
BotCentral
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Issuance of shares of common stock in connection with acquisition	0	$ 0	$ 1,000
Issuance of shares of common stock in connection with acquisition (in shares)			85,861
Conversable Sep 27 2018
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Issuance of shares of common stock in connection with acquisition	0	0	$ 2,850
Issuance of shares of common stock in connection with acquisition (in shares)			115,385
Conversable Inc
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair value of contingent earn-out in connection with the acquisition recorded in accrued expenses	0	0	$ 1,496
AdvantageTec
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Issuance of shares of common stock in connection with acquisition	0	0	$ 4,300
Issuance of shares of common stock in connection with acquisition (in shares)			178,082
Fair value of contingent earn-out in connection with the acquisition recorded in accrued expenses	0	0	$ 876
Issuance of shares of common stock as earn-out payment in connection with AdvantageTec Inc.	$ 293	$ 0	$ 0