CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Earnings (Deficit)	Total
Balances at Dec. 31, 2013	$ 221,124	$ 347	$ (7)	$ (84,048)	$ 137,416
Balances (in shares) at Dec. 31, 2013	57,369,683
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 8,370				8,370
Issuance of common stock upon exercise of options (in shares)	1,515,023
Issuance of common stock under employee stock purchase plan	$ 1,536				1,536
Issuance of common stock under employee stock purchase plan (in shares)	177,036
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)	231,686
Stock-based compensation	$ 8,931				8,931
Equity component of convertible debt issued, net of tax		73,272			73,272
Windfall tax benefit		3,190			3,190
Net income (loss)				131,762	131,762
Unrealized gains (losses) on available-for-sale securities, net of tax			(30)		(30)
Balances at Dec. 31, 2014	$ 239,961	76,809	(37)	47,714	364,447
Balances (in shares) at Dec. 31, 2014	59,293,428
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 7,860				$ 7,860
Issuance of common stock upon exercise of options (in shares)	1,137,303				1,141,345
Issuance of common stock under employee stock purchase plan	$ 2,462				$ 2,462
Issuance of common stock under employee stock purchase plan (in shares)	164,674
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)	191,904
Stock-based compensation	$ 14,228				14,228
Shares withheld for payment of employee's withholding tax liability		(2,812)			(2,812)
Windfall tax benefit		4,625			4,625
Net income (loss)				(75,738)	(75,738)
Unrealized gains (losses) on available-for-sale securities, net of tax			(17)		(17)
Balances at Dec. 31, 2015	$ 264,511	78,622	(54)	(28,024)	$ 315,055
Balances (in shares) at Dec. 31, 2015	60,787,309				60,787,309
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 6,693				$ 6,693
Issuance of common stock upon exercise of options (in shares)	715,655				711,863
Issuance of common stock under employee stock purchase plan	$ 3,258				$ 3,258
Issuance of common stock under employee stock purchase plan (in shares)	201,264
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)	261,960
Stock-based compensation	$ 17,172				17,172
Shares withheld for payment of employee's withholding tax liability		(3,342)			(3,342)
Windfall tax benefit		637			637
Net income (loss)				(88,720)	(88,720)
Unrealized gains (losses) on available-for-sale securities, net of tax			35		35
Balances at Dec. 31, 2016	$ 291,634	$ 75,917	$ (19)	$ (116,744)	$ 250,788
Balances (in shares) at Dec. 31, 2016	61,966,188				61,966,188