CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	2019 Convertible Senior Notes	2023 Convertible Senior Notes	Common Stock	Additional paid-in capital	Additional paid-in capital 2019 Convertible Senior Notes	Additional paid-in capital 2023 Convertible Senior Notes	Accumulated other comprehensive income (loss)	Accumulated deficit
Balance at beginning of period (shares) at Dec. 31, 2016				20,909,301
Balance at beginning of period at Dec. 31, 2016	$ 341,290			$ 21	$ 769,653			$ 2,743	$ (431,127)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock compensation plans, net (shares)				253,364
Issuance of common stock under employee stock compensation plans, net	(5,558)				(5,558)
Reclassification of equity component of currently redeemable convertible notes	10,704				10,704
Share-based compensation	$ 24,916				24,916
Repurchase of common stock (shares)	(14,000)			(14,000)
Repurchase of common stock	$ (1,966)				(1,966)
Other comprehensive income (loss)	(257)							(257)
Foreign currency translation adjustment	0
Net income (loss)	12,556								12,556
Balance at end of period (shares) at Dec. 31, 2017				21,148,665
Balance at end of period at Dec. 31, 2017	399,788			$ 21	798,205			2,486	(400,924)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock compensation plans, net (shares)				399,116
Issuance of common stock under employee stock compensation plans, net	16,417				16,417
Reclassification of equity component of currently redeemable convertible notes	18,859				18,859
Share-based compensation	$ 20,846				20,846
Repurchase of common stock (shares)	(782,248)			(782,248)
Repurchase of common stock	$ (127,481)				(127,481)
Other comprehensive income (loss)	73							73
Convertible bond hedge and warrant transactions, net of tax		$ (1,559)	$ (1,807)			$ (1,559)	$ (1,807)
Loss on settlement of Notes		3,187				3,187
Warrant repurchase		(30,472)				(30,472)
Loss on repurchase of warrants		1,792				1,792
Tax effect for Notes transactions		$ (1,680)	(3,181)			$ (1,680)	(3,181)
Warrant derivative			$ 97,805				$ 97,805
Foreign currency translation adjustment	(921)							(921)
Other tax adjustments	346				183				163
Net income (loss)	143,321								143,321
Balance at end of period (shares) at Dec. 31, 2018				20,765,533
Balance at end of period at Dec. 31, 2018	560,914			$ 21	791,114			(1,024)	(229,197)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock compensation plans, net (shares)				179,838
Issuance of common stock under employee stock compensation plans, net	(1,421)				(1,421)
Share-based compensation	$ 24,515				24,515
Repurchase of common stock (shares)	(4,122,133)			(4,122,133)
Repurchase of common stock	$ (448,433)			$ (4)	(448,429)
Unrealized net gain on available-for-sale securities, net of deferred tax	200							200
Foreign currency translation adjustment	608							608
Other tax adjustments	1,547				1,547
Net income (loss)	629,302								629,302
Balance at end of period (shares) at Dec. 31, 2019				16,823,238
Balance at end of period at Dec. 31, 2019	$ 767,232			$ 17	$ 367,326			$ (216)	$ 400,105