CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Earnings (Deficit)	Accumulated Other Comprehensive Loss	Convertible debt Convertible Senior Notes, 2.5%	Convertible debt Convertible Senior Notes, 2.5% Additional Paid-In Capital	Convertible debt Convertible Senior Notes, 5.0%	Convertible debt Convertible Senior Notes, 5.0% Additional Paid-In Capital
Balances at Dec. 31, 2016	$ 250,788	$ 6	$ 367,545	$ (116,744)	$ (19)
Balances (in shares) at Dec. 31, 2016		61,966,000
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	6,979	$ 0	6,979
Issuance of common stock upon exercise of options (in shares)		1,001,000
Issuance of common stock under employee stock purchase plan	1,960	$ 0	1,960
Issuance of common stock under employee stock purchase plan (in shares)		262,000
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		171,000
Stock-based compensation	13,016		13,016
Shares withheld for payment of employee's withholding tax liability	(753)		(753)
Net income (loss)	(102,496)			(102,496)
Unrealized gain on available-for-sale securities	14				14
Balances at Dec. 31, 2017	169,508	$ 6	389,015	(219,508)	(5)
Balances (in shares) at Dec. 31, 2017		63,400,000
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 1,493	$ 0	1,493
Issuance of common stock upon exercise of options (in shares)	278,000	278,000
Issuance of common stock under employee stock purchase plan	$ 527	$ 0	527
Issuance of common stock under employee stock purchase plan (in shares)		107,000
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		400,000
Stock-based compensation	12,585		12,585
Shares withheld for payment of employee's withholding tax liability	(686)		(686)
Net income (loss)	36,908			36,908
Balances at Dec. 31, 2018	$ 220,335	$ 6	402,934	(182,600)	(5)
Balances (in shares) at Dec. 31, 2018	64,185,224	64,185,000
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 25	$ 0	25
Issuance of common stock upon exercise of options (in shares)		14,000
Issuance of common stock under employee stock purchase plan	226	$ 0	226
Issuance of common stock under employee stock purchase plan (in shares)		169,000
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		703,000
Stock-based compensation	10,596		10,596
Issuance of common stock in conjunction with the Convertible Note Exchange (in shares)		15,817,000
Issuance of common stock in conjunction with the Convertible Note Exchange	25,307	$ 2	25,305
Reacquisition of equity component of debt, net of tax						$ (4,763)	$ (4,763)	$ 23,999	$ 23,999
Shares withheld for payment of employee's withholding tax liability	(571)		(571)
Net income (loss)	(217,201)			(217,201)
Unrealized gain on available-for-sale securities	5				5
Balances at Dec. 31, 2019	$ 57,958	$ 8	$ 457,751	$ (399,801)	$ 0
Balances (in shares) at Dec. 31, 2019	80,888,134	80,888,000