Stockholders' Equity (Details 5) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income	$ 115,935	$ (25,237)	$ 111,852	$ 137,524	$ (30,314)	$ 62,685	$ 79,864	$ 62,325	$ 340,074	$ 174,560	$ 304,442
Denominator:
Weighted average outstanding shares - basic									48,176	50,076	52,093
Effect of dilutive securities:
Convertible notes (in shares)									2,630	1,736	218
Warrants (in shares)									1,910	276
Stock options and employee stock purchase plan (in shares)									1,439	1,143	969
Weighted average shares - diluted									54,155	53,231	53,280
Basic
Net (loss) income per share-basic (in dollars per share)	$ 2.44	$ (0.53)	$ 2.35	$ 2.73	$ (0.60)	$ 1.25	$ 1.60	$ 1.24	$ 7.06	$ 3.49	$ 5.84
Diluted
Net (loss) income per share-diluted (in dollars per share)	$ 2.17	$ (0.53)	$ 2.10	$ 2.43	$ (0.60)	$ 1.17	$ 1.52	$ 1.19	$ 6.28	$ 3.28	$ 5.71
Stock options and warrants excluded from calculation (in shares)									9,273	11,210	11,862