CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' DEFICIT (Unaudited) - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Contributed capital	Contributed capital Common stock	Accumulated deficit	Accumulated deficit Cumulative effect of accounting changes	Treasury stock	Accumulated other comprehensive (loss) income
Beginning Balance (shares) at Dec. 31, 2019		0	54,709,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (shares)			2,287,000
Issuance of common stock under employee purchase plan (shares)			31,000
Ending Balance (shares) at Sep. 30, 2020		0	57,027,000
Beginning Balance, amount at Dec. 31, 2019		$ 0	$ 55	$ 452,344		$ (414,653)	$ (105)	$ (45,067)	$ (58)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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)
Net unrealized (loss) gain on debt securities available-for-sale	62								62
Foreign currency translation adjustment	90								90
Ending Balance, amount at Sep. 30, 2020	(49,668)	$ 0	$ 57	469,302		(474,054)		(45,067)	94
Beginning Balance (shares) at Jun. 30, 2020		0	56,249,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (shares)			770,000
Issuance of common stock under employee purchase plan (shares)			8,000
Ending Balance (shares) at Sep. 30, 2020		0	57,027,000
Beginning Balance, amount at Jun. 30, 2020		$ 0	$ 56	463,178		(455,297)		(45,067)	140
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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)
Net unrealized (loss) gain on debt securities available-for-sale	(117)								(117)
Foreign currency translation adjustment	71								71
Ending Balance, amount at Sep. 30, 2020	$ (49,668)	$ 0	$ 57	469,302		(474,054)		(45,067)	94
Beginning Balance (shares) at Dec. 31, 2020		0	57,608,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		2,636,000	2,937,000
Exercise of options (shares)	391,362		1,052,000
Issuance of common stock under employee purchase plan (shares)			37,000
Rescission of common stock (shares)			(2,643,000)
Issuance of shares in exchange for Convertible Senior Notes (shares)			5,946,000
Ending Balance (shares) at Sep. 30, 2021		2,636,000	64,937,000
Beginning Balance, amount at Dec. 31, 2020	$ (62,812)	$ 0	$ 58	475,072		(492,966)		(45,067)	91
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of stock		3	3		$ 22,637
Exercise of options			1	1,455
Rescission of common stock			(3)
Issuance of shares in exchange for Convertible Senior Notes			6	34,539
Issuance of common stock under employee purchase plan				245
Equity-based compensation				19,186
Net loss	(54,899)					(54,899)
Net unrealized (loss) gain on debt securities available-for-sale	(21)								(21)
Foreign currency translation adjustment	(87)								(87)
Ending Balance, amount at Sep. 30, 2021	(39,747)	$ 3	$ 65	553,134		(547,865)		(45,067)	(17)
Beginning Balance (shares) at Jun. 30, 2021		0	61,489,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)		2,636,000	67,000
Exercise of options (shares)			62,000
Issuance of common stock under employee purchase plan (shares)			16,000
Rescission of common stock (shares)			(2,643,000)
Issuance of shares in exchange for Convertible Senior Notes (shares)			5,946,000
Ending Balance (shares) at Sep. 30, 2021		2,636,000	64,937,000
Beginning Balance, amount at Jun. 30, 2021		$ 0	$ 61	514,122		(538,879)		(45,067)	13
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from issuance of stock		3	1		$ 517
Exercise of options				234
Rescission of common stock			(3)
Issuance of shares in exchange for Convertible Senior Notes			6	34,539
Issuance of common stock under employee purchase plan				84
Equity-based compensation				3,638
Net loss	(8,986)					(8,986)
Net unrealized (loss) gain on debt securities available-for-sale	(3)								(3)
Foreign currency translation adjustment	(27)								(27)
Ending Balance, amount at Sep. 30, 2021	$ (39,747)	$ 3	$ 65	$ 553,134		$ (547,865)		$ (45,067)	$ (17)