CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' DEFICIT - USD ($) $ in Thousands	Total	Common stock	Contributed capital	Accumulated deficit	Accumulated deficit Cumulative effect of accounting changes	Treasury stock	Accumulated other comprehensive (loss) income
Beginning Balance (shares) at Dec. 31, 2019		54,709,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (shares)		1,517,000
Issuance of common stock under employee purchase plan (shares)		23,000
Ending Balance (shares) at Jun. 30, 2020		56,249,000
Beginning Balance, amount at Dec. 31, 2019		$ 55	$ 452,344	$ (414,653)	$ (105)	$ (45,067)	$ (58)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options		1	3,031
Issuance of common stock under employee purchase plan			215
Equity-based compensation			7,588
Net loss	$ (40,539)			(40,539)
Net unrealized (loss) gain on debt securities available-for-sale	179						179
Foreign currency translation adjustment	19						19
Ending Balance, amount at Jun. 30, 2020	(36,990)	$ 56	463,178	(455,297)		(45,067)	140
Beginning Balance (shares) at Mar. 31, 2020		54,994,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (shares)		1,247,000
Issuance of common stock under employee purchase plan (shares)		8,000
Ending Balance (shares) at Jun. 30, 2020		56,249,000
Beginning Balance, amount at Mar. 31, 2020		$ 55	457,987	(436,067)		(45,067)	150
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options		1	1,713
Issuance of common stock under employee purchase plan			104
Equity-based compensation			3,374
Net loss	(19,230)			(19,230)
Net unrealized (loss) gain on debt securities available-for-sale	(44)						(44)
Foreign currency translation adjustment	34						34
Ending Balance, amount at Jun. 30, 2020	$ (36,990)	$ 56	463,178	(455,297)		(45,067)	140
Beginning Balance (shares) at Dec. 31, 2020		57,608,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		2,870,000
Exercise of options (shares)	337,393	990,000
Issuance of common stock under employee purchase plan (shares)		21,000
Ending Balance (shares) at Jun. 30, 2021		61,489,000
Beginning Balance, amount at Dec. 31, 2020	$ (62,812)	$ 58	475,072	(492,966)		(45,067)	91
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of common stock		2	22,120
Exercise of options		1	1,221
Issuance of common stock under employee purchase plan			161
Equity-based compensation			15,548
Net loss	(45,913)			(45,913)
Net unrealized (loss) gain on debt securities available-for-sale	(18)						(18)
Foreign currency translation adjustment	(60)						(60)
Ending Balance, amount at Jun. 30, 2021	(69,750)	$ 61	514,122	(538,879)		(45,067)	13
Beginning Balance (shares) at Mar. 31, 2021		59,561,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		1,481,000
Exercise of options (shares)		436,000
Issuance of common stock under employee purchase plan (shares)		11,000
Ending Balance (shares) at Jun. 30, 2021		61,489,000
Beginning Balance, amount at Mar. 31, 2021		$ 60	495,857	(517,205)		(45,067)	(9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of common stock		1	11,455
Exercise of options			113
Issuance of common stock under employee purchase plan			81
Equity-based compensation			6,616
Net loss	(21,674)			(21,674)
Net unrealized (loss) gain on debt securities available-for-sale	1						1
Foreign currency translation adjustment	21						21
Ending Balance, amount at Jun. 30, 2021	$ (69,750)	$ 61	$ 514,122	$ (538,879)		$ (45,067)	$ 13