Stockholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income	$ 137,524	$ 62,325
Denominator:
Weighted average outstanding shares - basic	50,402	50,209
Effect of dilutive securities:
Convertible notes (in shares)	2,798	826
Warrants (in shares)	1,780
Stock options and employee stock purchase plan (in shares)	1,677	1,341
Weighted average shares - diluted	56,657	52,376
Earnings per common share:
Basic (in dollars per share)	$ 2.73	$ 1.24
Diluted (in dollars per share)	$ 2.43	$ 1.19
Stock options and warrants excluded from calculation (in shares)	9,705	11,026