Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 264,804	$ 210,398	$ 642,407	$ 481,062
Interest on Convertible Debt, Net of Tax	0	145	397	0
Net Income (Loss) Available to Common Stockholders, Diluted	$ 264,804	$ 210,543	$ 642,804	$ 481,062
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	104,833	103,348	104,586	102,825
Effect of dilutive securities (in shares):
Stock options	10,156	9,632	10,340	9,449
Restricted stock	479	481	474	475
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	0	308	81	0
Warrants	998	2,175	1,086	2,395
Dilutive potential shares	11,633	12,596	11,981	12,319
Weighted average shares - diluted (in shares)	116,466	115,944	116,567	115,144
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 2.53	$ 2.04	$ 6.14	$ 4.68
Net income per share - diluted (in dollars per share)	$ 2.27	$ 1.82	$ 5.51	$ 4.18
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	7,687	594	7,842	3,388
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	19	0	19	0
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	3	0	0	1,253