CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common stock	Contributed capital	Accumulated deficit	Accumulated deficit Adjustment	Treasury stock	Accumulated other comprehensive (loss) income
Beginning Balance (shares) at Dec. 31, 2018		54,232,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		56,000
Exercise of options (shares)		334,000
Issuance of common stock under employee purchase plan (shares)		19,000
Ending Balance (shares) at Sep. 30, 2019		54,641,000
Beginning Balance, amount at Dec. 31, 2018		$ 54	$ 432,885	$ (330,348)	$ 0	$ (45,067)	$ (149)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of common stock			1,000
Exercise of options		1	4,879
Issuance of common stock under employee purchase plan			362
Equity-based compensation			9,483
Net loss	$ (62,970)			(62,970)
Unrealized loss on available-for-sale securities	229						229
Foreign currency translation adjustment	(139)						(139)
Ending Balance, amount at Sep. 30, 2019	10,220	$ 55	448,609	(393,318)		(45,067)	(59)
Beginning Balance (shares) at Jun. 30, 2019		54,512,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		56,000
Exercise of options (shares)		66,000
Issuance of common stock under employee purchase plan (shares)		7,000
Ending Balance (shares) at Sep. 30, 2019		54,641,000
Beginning Balance, amount at Jun. 30, 2019		$ 55	443,857	(372,884)		(45,067)	44
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of common stock			1,000
Exercise of options		0	510
Issuance of common stock under employee purchase plan			112
Equity-based compensation			3,130
Net loss	(20,434)			(20,434)
Unrealized loss on available-for-sale securities	10						10
Foreign currency translation adjustment	(113)						(113)
Ending Balance, amount at Sep. 30, 2019	$ 10,220	$ 55	448,609	(393,318)		(45,067)	(59)
Beginning Balance (shares) at Dec. 31, 2019		54,709,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		0
Exercise of options (shares)	2,219,281	2,287,000
Issuance of common stock under employee purchase plan (shares)		31,000
Ending Balance (shares) at Sep. 30, 2020		57,027,000
Beginning Balance, amount at Dec. 31, 2019	$ (7,379)	$ 55	452,344	(414,653)	$ (105)	(45,067)	(58)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of common stock			0
Exercise of options		2	4,458
Issuance of common stock under employee purchase plan			294
Equity-based compensation			12,206
Net loss	(59,296)			(59,296)
Unrealized loss on available-for-sale securities	62						62
Foreign currency translation adjustment	90						90
Ending Balance, amount at Sep. 30, 2020	(49,668)	$ 57	469,302	(474,054)		(45,067)	94
Beginning Balance (shares) at Jun. 30, 2020		56,249,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		0
Exercise of options (shares)		770,000
Issuance of common stock under employee purchase plan (shares)		8,000
Ending Balance (shares) at Sep. 30, 2020		57,027,000
Beginning Balance, amount at Jun. 30, 2020		$ 56	463,178	(455,297)		(45,067)	140
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of common stock			0
Exercise of options		1	1,427
Issuance of common stock under employee purchase plan			79
Equity-based compensation			4,618
Net loss	(18,757)			(18,757)
Unrealized loss on available-for-sale securities	(117)						(117)
Foreign currency translation adjustment	71						71
Ending Balance, amount at Sep. 30, 2020	$ (49,668)	$ 57	$ 469,302	$ (474,054)		$ (45,067)	$ 94