Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Treasury Stock
Beginning Balance, shares at Dec. 31, 2018		53,955
Balance at beginning of period at Dec. 31, 2018	$ 151,934	$ 1,482	$ 876,073	$ (753)	$ (684,882)	$ (39,986)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	11,181		11,181
Issuance of common stock under equity incentive plans, net of forfeitures (in shares)		2,493
Issuance of common stock under equity incentive plans, net of forfeitures	8,708	$ 63	8,645
Net income (loss)	(17,694)				(17,694)
Other comprehensive income (loss)	(101)			(101)
Ending Balance, shares at Dec. 31, 2019		56,448
Balance at end of period at Dec. 31, 2019	154,028	$ 1,545	895,899	(854)	(702,576)	(39,986)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	13,960		13,960
Issuance of common stock under equity incentive plans, net of forfeitures (in shares)		2,454
Issuance of common stock under equity incentive plans, net of forfeitures	18,127	$ 60	18,067
Issuance of common stock in connection with public offering, net of expenses (in shares)		3,220
Issuance of common stock in connection with public offering, net of expenses	60,063	$ 82	59,981
Treasury stock retirement	0	$ (134)	(39,852)			39,986
Net income (loss)	33,484				33,484
Other comprehensive income (loss)	$ 663			663
Ending Balance, shares at Dec. 31, 2020	62,122	62,122
Balance at end of period at Dec. 31, 2020	$ 280,325	$ 1,553	948,055	(191)	(669,092)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	24,230		24,230
Issuance of common stock under equity incentive plans, net of forfeitures (in shares)		2,152
Issuance of common stock under equity incentive plans, net of forfeitures	25,624	$ 54	25,570
Net income (loss)	238,378				238,378
Other comprehensive income (loss)	$ (129)			(129)
Ending Balance, shares at Dec. 31, 2021	64,274	64,274
Balance at end of period at Dec. 31, 2021	$ 568,428	$ 1,607	$ 997,855	$ (320)	$ (430,714)	$ 0