CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2011	$ 215,279	$ 6	$ (10,461)	$ 375,525	$ (149,791)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	8,611			8,611
Surrender of stock to satisfy minimum tax withholding	(174)		(174)
Issuance of treasury stock for restricted stock vesting	0		324	(324)
Compensation under employee stock compensation plan	4,986			4,986
Net income (loss)	64,707				64,707
Balance at Dec. 31, 2012	293,409	6	(10,311)	388,798	(85,084)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds of public stock offering	118,382	1		118,381
Exercise of stock options	2,549			2,549
Compensation under employee stock compensation plan	9,498			9,498
Exercise of warrants	399			399
Net income (loss)	(69,654)				(69,654)
Balance at Dec. 31, 2013	354,583	7	(10,311)	519,625	(154,738)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	1,468	1		1,467
Surrender of stock to satisfy minimum tax withholding	(368)		(368)
Compensation under employee stock compensation plan	8,590			8,590
Net income (loss)	(147,468)				(147,468)
Balance at Dec. 31, 2014	$ 216,805	$ 8	$ (10,679)	$ 529,682	$ (302,206)