Net Income Per Share (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 79,720,000	$ 141,306,000	$ 237,898,000	$ 327,556,000
Interest on Convertible Debt, Net of Tax	2,803,000	4,678,000	0	13,857,000
Net Income (Loss) Available to Common Stockholders, Diluted	$ 82,523,000	$ 145,984,000	$ 237,898,000	$ 341,413,000
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	100,796	98,226	100,325	97,602
Effect of dilutive securities (in shares):
Stock options	9,377	10,379	9,515	10,220
Restricted stock	430	462	413	415
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	4,033	4,761	0	4,761
Warrants	2,787	2,885	2,950	2,556
Dilutive potential shares	16,627	18,487	12,878	17,952
Weighted average shares - diluted (in shares)	117,423	116,713	113,203	115,554
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 0.79	$ 1.44	$ 2.37	$ 3.36
Net income per share - diluted (in dollars per share)	$ 0.70	$ 1.25	$ 2.10	$ 2.95
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	1,227	135	3,741	1,265
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares			4,483	0