Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 141,306	$ 191,468	$ 327,556	$ 279,862
Interest on Convertible Debt, Net of Tax	4,678	7,374	13,857
Net Income - diluted	$ 145,984	$ 198,842	$ 341,413	$ 279,862
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares - basic (in shares)	98,226	95,012	97,602	94,349
Effect of dilutive securities (in shares):
Stock options	10,379	14,106	10,220	14,080
Restricted stock	462	797	415	699
Convertible senior notes	4,761	4,761	4,761
Warrants	2,885	1,154	2,556	652
Dilutive potential shares	18,487	20,818	17,952	15,431
Weighted average shares - diluted (in shares)	116,713	115,830	115,554	109,780
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic (in dollars per share)	$ 1.44	$ 2.02	$ 3.36	$ 2.97
Net income per share - diluted (in dollars per share)	$ 1.25	$ 1.72	$ 2.95	$ 2.55
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	135	175	1,265	91
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares				4,761