Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 65,443	$ 98,874
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	98,709	96,878
Effect of dilutive securities (in shares):
Stock options	9,879	10,276
Restricted stock	401	325
Warrants	3,162	1,890
Dilutive potential shares	13,442	12,491
Weighted average shares - diluted (in shares)	112,151	109,369
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 0.66	$ 1.02
Net income per share - diluted (in dollars per share)	$ 0.58	$ 0.90
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	3,646	3,868
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	4,761	4,761