Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 196,218	$ 194,643	$ 377,603	$ 270,664
Interest on Convertible Debt, Net of Tax			373	0
Net Income (Loss) Available to Common Stockholders, Diluted	$ 186,122	$ 194,643	$ 377,976	$ 270,664
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	104,633	102,886	104,462	102,558
Effect of dilutive securities (in shares):
Stock options	10,141	9,438	10,433	9,441
Restricted stock	473	474	471	471
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities			121	0
Warrants	984	2,461	1,130	2,492
Dilutive potential shares	11,598	12,373	12,155	12,404
Weighted average shares - diluted (in shares)	116,231	115,259	116,617	114,962
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 1.88	$ 1.89	$ 3.61	$ 2.64
Net income per share - diluted (in dollars per share)	$ 1.69	$ 1.69	$ 3.24	$ 2.35
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	7,904	3,366	7,830	3,370
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	20	0	19	0
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	96	1,539	0	1,733