Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 87,376	$ 76,743	$ 186,250	$ 88,394
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares - basic (in shares)	97,700	94,589	97,289	94,017
Effect of dilutive securities (in shares):
Stock options	10,291	14,055	10,296	13,964
Restricted stock	424	692	383	676
Warrants	2,645	831	2,337	341
Dilutive potential shares	13,360	15,578	13,016	14,981
Weighted average shares - diluted (in shares)	111,060	110,167	110,305	108,998
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic (in dollars per share)	$ 0.89	$ 0.81	$ 1.91	$ 0.94
Net income per share - diluted (in dollars per share)	$ 0.79	$ 0.70	$ 1.69	$ 0.81
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	1,247	89	3,599	47
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares				11
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	4,761	4,761	4,761	4,761