Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator, in thousands
Net income (loss) used for calculation of basic EPS									$ 14,016	$ 19,871	$ (92,273)
Interest expense on convertible debt									1,229	4,963
Change in fair value of derivative liabilities									(589)	(2,809)
Loss on extinguishment of debt									2,338	2,592
Loss on extinguishment of outstanding debt, as if converted									(2,494)	(8,315)
Total adjustments									484	(3,569)
Net income used for calculation of diluted EPS									$ 14,500	$ 16,302	$ (92,273)
Denominator
Weighted average shares outstanding, basic									47,485,258	42,260,896	31,848,299
Effect of dilutive potential common shares
Shares underlying Convertible Senior Secured Notes									2,459,009	7,090,722
Shares issuable to settle interest make-whole derivatives									804,507	904,618
Warrants to purchase common stock										20,499
Stock options, stock appreciation rights, and non-vested stock options									411,606	306,776
Total potential dilutive common shares									3,675,122	8,322,615
Weighted average shares outstanding, diluted									51,160,380	50,583,511	31,848,299
Net income (loss) per share, basic	$ 0.14	$ 0.09	$ 0.04	$ 0.02	$ 0.10	$ 0.65	$ 0.08	$ (0.38)	$ 0.30	$ 0.47	$ (2.90)
Net income (loss) per share, diluted	$ 0.14	$ 0.08	$ 0.03	$ 0.02	$ 0.10	$ 0.39	$ 0.08	$ (0.38)	$ 0.28	$ 0.32	$ (2.90)
7.50% Convertible Senior Secured Notes due 2019
Loss Per Share
Common stock equivalents excluded in the calculation of diluted loss per share											6,219,782
Warrants to purchase common stock.
Loss Per Share
Common stock equivalents excluded in the calculation of diluted loss per share											13,388
Stock Options, Stock Appreciation Rights and Non-Vested Stock Options and ESPP awards
Loss Per Share
Common stock equivalents excluded in the calculation of diluted loss per share											151,737