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, 2012	$ 211,266		$ 31	$ (127,361)	$ 83,936
Balances (in shares) at Dec. 31, 2012	56,383,713
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 2,782				2,782
Issuance of common stock upon exercise of options (in shares)	621,090
Issuance of common stock under employee stock purchase plan	$ 966				966
Issuance of common stock under employee stock purchase plan (in shares)	222,062
Issuance of common stock in conjunction with vesting of restricted stock units	$ 765				765
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)	142,818
Stock-based compensation	$ 5,345				5,345
Windfall tax benefit		$ 347			347
Net income (loss)				43,313	43,313
Unrealized gain (loss) on available-for-sale securities			(38)		(38)
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				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	$ 1,799				1,799
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)	231,686
Stock-based compensation	$ 7,132				7,132
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 gain (loss) on available-for-sale securities			(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				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	$ 4,111				4,111
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)	191,904
Stock-based compensation	$ 10,117				10,117
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 gain (loss) on available-for-sale securities			(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