CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Conversion of Class B Common Stock To Class A Common Stock	Common Stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Redeemable convertible preferred stock	Class A common stock	Class A common stock Common Stock	Class A common stock Common Stock Conversion of Class B Common Stock To Class A Common Stock	Class B common stock	Class B common stock Common Stock	Class B common stock Common Stock Conversion of Class B Common Stock To Class A Common Stock
Beginning balance (in shares) at Dec. 31, 2018							165,658,000
Beginning balance at Dec. 31, 2018							$ 331,521
Ending balance (in shares) at Jun. 30, 2019							165,658,000
Ending balance at Jun. 30, 2019							$ 331,521
Beginning balance (in shares) at Dec. 31, 2018			91,542,000
Beginning balance at Dec. 31, 2018	$ (113,505)		$ 85	$ 82,345	$ (195,878)	$ (57)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with acquisition (in shares)			7,000
Issuance of common stock in connection with acquisition	18			18
Issuance of common stock upon exercise of stock options (in shares)			581,000
Issuance of common stock upon exercise of stock options	1,067		$ 1	1,066
Repurchases of unvested common stock (in shares)			(40,000)
Issuance of common stock related to early exercised stock options (in shares)			596,000
Vesting of shares issued upon early exercise of stock options	1,438			1,438
Stock-based compensation	2,244			2,244
Net loss	(36,820)		$ (36,820)		(36,820)
Other comprehensive income (loss)	123
Ending balance (in shares) at Jun. 30, 2019			92,686,000
Ending balance at Jun. 30, 2019	(145,435)		$ 86	87,111	(232,698)	66
Beginning balance (in shares) at Mar. 31, 2019							165,658,000
Beginning balance at Mar. 31, 2019							$ 331,521
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)							0
Issuance of common stock in connection with acquisition							$ 0
Ending balance (in shares) at Jun. 30, 2019							165,658,000
Ending balance at Jun. 30, 2019							$ 331,521
Beginning balance (in shares) at Mar. 31, 2019			92,293,000
Beginning balance at Mar. 31, 2019	(128,224)		$ 85	84,668	(212,992)	15
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			235,000
Issuance of common stock upon exercise of stock options	386		$ 1	385
Repurchases of unvested common stock (in shares)									(31,000)
Issuance of common stock related to early exercised stock options (in shares)			189,000
Vesting of shares issued upon early exercise of stock options	942			942
Stock-based compensation	1,116			1,116
Net loss	(19,706)		$ (19,706)		(19,706)
Other comprehensive income (loss)	51					51
Ending balance (in shares) at Jun. 30, 2019			92,686,000
Ending balance at Jun. 30, 2019	(145,435)		$ 86	87,111	(232,698)	66
Beginning balance (in shares) at Dec. 31, 2019							0
Beginning balance at Dec. 31, 2019							$ 0
Ending balance (in shares) at Jun. 30, 2020							0
Ending balance at Jun. 30, 2020							$ 0
Beginning balance (in shares) at Dec. 31, 2019								87,071,783	87,072,000		213,101,364	213,101,000
Beginning balance at Dec. 31, 2019	$ 725,828			1,027,179	(301,706)	61			$ 87			$ 207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with acquisition (in shares)	948,000								107,000
Issuance of common stock in connection with acquisition	$ 1,821			1,821
Issuance of unvested restricted stock in connection with acquisition (in shares)									841,000
Issuance of common stock upon exercise of stock options (in shares)	2,618,000											2,582,000
Issuance of common stock upon exercise of stock options	$ 4,335			4,333								$ 2
Repurchases of unvested common stock (in shares)									(37,000)
Issuance of common stock related to early exercised stock options (in shares)												36,000
Vesting of shares issued upon early exercise of stock options	2,511			2,509								$ 2
Issuance of common stock related to settlement of RSUs (in shares)									82,000			1,645,000
Issuance of common stock related to settlement of RSUs	1			(1)								$ 2
Tax withholding on RSU settlement (in shares)									(11,000)			(402,000)
Tax withholding on RSU settlement	(7,308)			(7,308)
Conversion of Class B to Class A common stock (in shares)										96,438,000			96,438,000
Conversion of Class B to Class A common stock		$ 0								$ 97			$ (97)
Equity component of convertible senior notes, net of issuance costs	200,812			200,812
Purchases of capped calls related to convertible senior notes	(67,333)			(67,333)
Common stock issued under employee stock purchase plan (in shares)									421,000
Common stock issued under employee stock purchase plan	5,447			5,447
Tax withholding on common stock issued under employee stock purchase plan (in shares)									(13,000)
Tax withholding on common stock issued under employee stock purchase plan	(376)			(376)
Stock-based compensation	27,042			27,042
Net loss	(58,881)				(58,881)				$ (26,404)			$ (32,477)
Other comprehensive income (loss)	1,163					1,163
Ending balance (in shares) at Jun. 30, 2020								184,900,249	184,900,000		120,523,936	120,524,000
Ending balance at Jun. 30, 2020	835,618			1,194,125	(360,031)	1,224			$ 184			$ 116
Beginning balance (in shares) at Mar. 31, 2020							0
Beginning balance at Mar. 31, 2020							$ 0
Ending balance (in shares) at Jun. 30, 2020							0
Ending balance at Jun. 30, 2020							$ 0
Beginning balance (in shares) at Mar. 31, 2020									154,622,000			148,735,000
Beginning balance at Mar. 31, 2020	706,352			1,038,544	(333,896)	1,407			$ 154			$ 143
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with acquisition	717
Issuance of common stock upon exercise of stock options (in shares)									0			1,079,000
Issuance of common stock upon exercise of stock options	1,660			1,659					$ 0			$ 1
Repurchases of unvested common stock (in shares)										(8,000)
Issuance of common stock related to early exercised stock options (in shares)												21,000
Vesting of shares issued upon early exercise of stock options	1,288			1,287								$ 1
Issuance of common stock related to settlement of RSUs (in shares)									50,000			522,000
Issuance of common stock related to settlement of RSUs	1			0								$ 1
Tax withholding on RSU settlement (in shares)									0			(5,000)
Tax withholding on RSU settlement	(193)			(193)
Conversion of Class B to Class A common stock (in shares)										29,828,000			29,828,000
Conversion of Class B to Class A common stock		$ 0								$ 30			$ (30)
Equity component of convertible senior notes, net of issuance costs	200,812			200,812
Purchases of capped calls related to convertible senior notes	(67,333)			(67,333)
Common stock issued under employee stock purchase plan (in shares)									421,000
Common stock issued under employee stock purchase plan	5,447			5,447
Tax withholding on common stock issued under employee stock purchase plan (in shares)									(13,000)
Tax withholding on common stock issued under employee stock purchase plan	(376)			(376)
Stock-based compensation	13,561			13,561
Net loss	(26,135)				(26,135)				$ (14,773)			$ (11,362)
Other comprehensive income (loss)	(183)					(183)
Ending balance (in shares) at Jun. 30, 2020								184,900,249	184,900,000		120,523,936	120,524,000
Ending balance at Jun. 30, 2020	$ 835,618			$ 1,194,125	$ (360,031)	$ 1,224			$ 184			$ 116