CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	2025 Convertible Notes	2022 Convertible Notes	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital 2025 Convertible Notes	Additional Paid-in Capital 2022 Convertible Notes	Accumulated Deficit	Treasury Stock
Beginning balance at Dec. 31, 2019	$ 402,326			$ 157	$ 1,177,984			$ (592,654)	$ (183,161)
Beginning balance (in shares) at Dec. 31, 2019				15,677					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	14,401							14,401
Non-cash compensation	11,917				11,917
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(5,087)				(5,087)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)				27
Other	0				(1)			1
Ending balance at Mar. 31, 2020	423,557			$ 157	1,184,813			(578,252)	$ (183,161)
Ending balance (in shares) at Mar. 31, 2020				15,704					2,641
Beginning balance at Dec. 31, 2019	402,326			$ 157	1,177,984			(592,654)	$ (183,161)
Beginning balance (in shares) at Dec. 31, 2019				15,677					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	(39,999)
Ending balance at Sep. 30, 2020	361,009			$ 158	1,176,664			(632,652)	$ (183,161)
Ending balance (in shares) at Sep. 30, 2020				15,759					2,641
Beginning balance at Mar. 31, 2020	423,557			$ 157	1,184,813			(578,252)	$ (183,161)
Beginning balance (in shares) at Mar. 31, 2020				15,704					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	(29,757)							(29,757)
Non-cash compensation	13,158				13,158
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(981)				(981)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)				27
Ending balance at Jun. 30, 2020	405,977			$ 157	1,196,990			(608,009)	$ (183,161)
Ending balance (in shares) at Jun. 30, 2020				15,731					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	(24,643)							(24,643)
Non-cash compensation	14,161				14,161
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	4,646			$ 1	4,645
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)				28
Issuance of 0.50% Convertible Senior Notes, net		$ 116,300				$ 116,300
Repurchase of 0.625% Convertible Senior Notes, net			$ (107,882)				$ (107,882)
Convertible note hedge transactions	(14,379)				(14,379)
Warrant transactions	(33,171)				(33,171)
Ending balance at Sep. 30, 2020	361,009			$ 158	1,176,664			(632,652)	$ (183,161)
Ending balance (in shares) at Sep. 30, 2020				15,759					2,641
Beginning balance at Dec. 31, 2020	364,761			$ 158	1,188,673			(640,909)	$ (183,161)
Beginning balance (in shares) at Dec. 31, 2020				15,766					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	19,049							19,049
Non-cash compensation	16,436				16,436
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(4,801)				(4,801)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)				31
Other	(2)				(2)
Ending balance at Mar. 31, 2021	395,443			$ 158	1,200,306			(621,860)	$ (183,161)
Ending balance (in shares) at Mar. 31, 2021				15,797					2,641
Beginning balance at Dec. 31, 2020	364,761			$ 158	1,188,673			(640,909)	$ (183,161)
Beginning balance (in shares) at Dec. 31, 2020				15,766					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	21,190
Ending balance at Sep. 30, 2021	431,082			$ 160	1,233,802			(619,719)	$ (183,161)
Ending balance (in shares) at Sep. 30, 2021				15,969					2,641
Beginning balance at Mar. 31, 2021	395,443			$ 158	1,200,306			(621,860)	$ (183,161)
Beginning balance (in shares) at Mar. 31, 2021				15,797					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	6,601							6,601
Non-cash compensation	18,294				18,294
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	30			$ 2	28
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)				159
Ending balance at Jun. 30, 2021	420,368			$ 160	1,218,628			(615,259)	$ (183,161)
Ending balance (in shares) at Jun. 30, 2021				15,956					2,641
Increase (Decrease) in Stockholders' Equity
Net income (loss) and comprehensive income (loss)	(4,460)							(4,460)
Non-cash compensation	17,074				17,074
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(1,894)			$ 0	(1,894)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)				13
Other	(6)				(6)
Ending balance at Sep. 30, 2021	$ 431,082			$ 160	$ 1,233,802			$ (619,719)	$ (183,161)
Ending balance (in shares) at Sep. 30, 2021				15,969					2,641