Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Net income (loss)	$ 96,806	$ 141,306	$ 87,376	$ 98,874	$ 470,407	[1]	$ 191,468	[1]	$ 76,743	[1]	$ 11,651	[1]	$ 424,362	$ 750,269	$ (221,760)
Effect of dilutive securities:
Convertible senior notes - interest expense related to contractual coupon interest rate and amortization of discount and note issuance costs													0	29,126	0
Net income (loss) - diluted													$ 424,362	$ 779,395	$ (221,760)
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic													97,917	94,685	90,610
Effect of dilutive securities (in shares):
Stock options													10,233	14,231	0
Restricted stock													433	715	0
Convertible senior notes													0	4,761	0
Warrants													2,707	990	0
Dilutive potential shares													13,373	20,697	0
Weighted average shares - diluted (in shares)													111,290	115,382	90,610
Earnings Per Share, Basic and Diluted [Abstract]
Net income (loss) per share - basic	$ 0.98	$ 1.44	$ 0.89	$ 1.02	$ 4.92		$ 2.02		$ 0.81		$ 0.12		$ 4.33	$ 7.92	$ (2.45)
Net income (loss) per share - diluted (in dollars per share)	$ 0.86	$ 1.25	$ 0.79	$ 0.90	$ 4.08		$ 1.72		$ 0.70		$ 0.11		$ 3.81	$ 6.75	$ (2.45)
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares													304	325	20,942
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares													0	0	846
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares													4,761	0	939
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares													0	0	939

[1] Net income for the quarter ended December 31, 2012 included an income tax benefit of $335.8 million, primarily attributable to the release of substantially all of the Company's valuation allowance against its deferred tax assets.