Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator, in thousands:
Net income (loss) used for calculation of basic EPS									$ 91,221	$ 13,944	$ (10,925)
Interest expense on convertible debt									543	1,229
Changes in fair value of derivative liabilities									(448)	(589)
Loss on extinguishment of debt									671	2,338
Loss on extinguishment of outstanding debt, as if converted									(1,182)	(2,494)
Total adjustments									(416)	484
Net income used for calculation of diluted EPS									$ 90,805	$ 14,428	$ (10,925)
Denominator:
Weighted average shares outstanding, basic									49,472,434	47,485,258	42,260,896
Effect of dilutive potential common shares:
Shares underlying Convertible Senior Secured Notes									1,222,363	2,459,009
Shares issuable to settle interest make-whole derivatives									71,537	804,507
Stock options and stock appreciation rights									942,649	411,606
Total potential dilutive common shares									2,236,549	3,675,122
Weighted average shares outstanding, diluted									51,708,983	51,160,380	42,260,896
Net income (loss) per share, basic	$ 0.29	$ 1.25	$ 0.21	$ 0.10	$ 0.14	$ 0.08	$ 0.05	$ 0.02	$ 1.84	$ 0.29	$ (0.26)
Net income (loss) per share, diluted	$ 0.26	$ 1.18	$ 0.18	$ 0.08	$ 0.14	$ 0.08	$ 0.04	$ 0.02	$ 1.76	$ 0.28	$ (0.26)
7.50% Convertible Senior Secured Notes due 2019
Loss per share
Common stock equivalents excluded in the calculation of diluted loss per share											7,995,340
Warrants to purchase common stock
Loss per share
Common stock equivalents excluded in the calculation of diluted loss per share										20,957	20,499
Stock options, stock appreciation rights, and ESPP awards
Loss per share
Common stock equivalents excluded in the calculation of diluted loss per share											306,776