Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 210,398	$ 90,095	$ 83,375	$ 481,062	$ 248,031	$ 338,126
Interest on Convertible Debt, Net of Tax	145		2,803
Net Income (Loss) Available to Common Stockholders, Diluted	$ 210,543		$ 86,178
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	103,348		100,796	102,825	100,325
Effect of dilutive securities (in shares):
Stock options	9,632		9,377	9,449	9,515
Restricted stock	481		430	475	413
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	308		4,033
Warrants	2,175		2,787	2,395	2,950
Dilutive potential shares	12,596		16,627	12,319	12,878
Weighted average shares - diluted (in shares)	115,944		117,423	115,144	113,203
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 2.04	$ 0.89	$ 0.83	$ 4.68	$ 2.47	$ 3.36
Net income per share - diluted (in dollars per share)	$ 1.82	$ 0.78	$ 0.73	$ 4.18	$ 2.19	$ 2.98
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	594		1,277	3,388	3,741
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares				1,253	4,483