Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2019	$ 578,694	$ 61	$ 1,316,795	$ 754	$ (738,916)
Beginning Balance, Shares at Dec. 31, 2019		60,644,380
Issuance of common stock upon exercise of stock options	967		967
Issuance of common stock upon exercise of stock options, Shares		33,937
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	(2,099)		(2,099)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		160,594
Issuance of common stock pursuant to ESPP purchases	1,870		1,870
Issuance of common stock pursuant to ESPP purchases, Shares		47,460
Stock-based compensation	16,705		16,705
Net unrealized gain (loss) on marketable securities	461			461
Net loss	(73,026)				(73,026)
Ending Balance at Mar. 31, 2020	523,572	$ 61	1,334,238	1,215	(811,942)
Ending Balance, Shares at Mar. 31, 2020		60,886,371
Beginning Balance at Dec. 31, 2019	578,694	$ 61	1,316,795	754	(738,916)
Beginning Balance, Shares at Dec. 31, 2019		60,644,380
Cumulative translation adjustment	0
Net loss	(125,866)
Ending Balance at Jun. 30, 2020	495,816	$ 61	1,359,310	1,227	(864,782)
Ending Balance, Shares at Jun. 30, 2020		61,330,987
Beginning Balance at Mar. 31, 2020	523,572	$ 61	1,334,238	1,215	(811,942)
Beginning Balance, Shares at Mar. 31, 2020		60,886,371
Issuance of common stock upon exercise of stock options	8,018		8,018
Issuance of common stock upon exercise of stock options, Shares		334,454
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	(74)		(74)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		110,162
Stock-based compensation	17,128		17,128
Net unrealized gain (loss) on marketable securities	12			12
Cumulative translation adjustment	0
Net loss	(52,840)				(52,840)
Ending Balance at Jun. 30, 2020	495,816	$ 61	1,359,310	1,227	(864,782)
Ending Balance, Shares at Jun. 30, 2020		61,330,987
Beginning Balance at Dec. 31, 2020	416,157	$ 62	1,402,262	302	(986,469)
Beginning Balance, Shares at Dec. 31, 2020		61,898,090
Issuance of common stock upon exercise of stock options	1,110		1,110
Issuance of common stock upon exercise of stock options, Shares		47,763
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	(1,897)		(1,897)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		229,087
Issuance of common stock pursuant to ESPP purchases	2,558		2,558
Issuance of common stock pursuant to ESPP purchases, Shares		65,110
Stock-based compensation	20,378		20,378
Net unrealized gain (loss) on marketable securities	(181)			(181)
Net loss	(74,930)				(74,930)
Ending Balance at Mar. 31, 2021	363,195	$ 62	1,424,411	121	(1,061,399)
Ending Balance, Shares at Mar. 31, 2021		62,240,050
Beginning Balance at Dec. 31, 2020	$ 416,157	$ 62	1,402,262	302	(986,469)
Beginning Balance, Shares at Dec. 31, 2020		61,898,090
Issuance of common stock upon exercise of stock options, Shares	76,338
Cumulative translation adjustment	$ 259
Net loss	(144,522)
Ending Balance at Jun. 30, 2021	315,766	$ 62	1,446,393	302	(1,130,991)
Ending Balance, Shares at Jun. 30, 2021		62,379,118
Beginning Balance at Mar. 31, 2021	363,195	$ 62	1,424,411	121	(1,061,399)
Beginning Balance, Shares at Mar. 31, 2021		62,240,050
Issuance of common stock upon exercise of stock options	403		403
Issuance of common stock upon exercise of stock options, Shares		28,575
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	(65)		(65)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		110,493
Stock-based compensation	21,644		21,644
Cumulative translation adjustment	259			259
Other comprehensive losses	(78)			(78)
Net loss	(69,592)				(69,592)
Ending Balance at Jun. 30, 2021	$ 315,766	$ 62	$ 1,446,393	$ 302	$ (1,130,991)
Ending Balance, Shares at Jun. 30, 2021		62,379,118