Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 165,736	$ 76,021
Interest on Convertible Debt, Net of Tax	56	0
Net Income (Loss) Available to Common Stockholders, Diluted	$ 165,792	$ 76,021
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	104,290	102,227
Effect of dilutive securities (in shares):
Stock options	8,147	9,313
Restricted stock	469	467
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	44	0
Warrants	1,278	2,512
Dilutive potential shares	9,938	12,292
Weighted average shares - diluted (in shares)	114,228	114,519
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 1.59	$ 0.74
Net income per share - diluted (in dollars per share)	$ 1.45	$ 0.66
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	7,539	3,673
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	19	0
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	0	1,929