Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 253,115	$ 264,804	$ 196,218	$ 181,385	$ 154,994	$ 210,398	$ 194,643	$ 76,021	$ 895,522	$ 636,056	$ 338,126
Dilutive Securities, Effect on Basic Earnings Per Share, Dilutive Convertible Securities									397	0	0
Net Income (Loss) Attributable to Parent, Diluted									$ 895,919	$ 636,056	$ 338,126
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic									104,719	103,061	100,612
Effect of dilutive securities (in shares):
Stock options									10,177	9,446	9,440
Restricted stock									474	477	425
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities									61	0	0
Warrants									936	2,246	2,936
Dilutive potential shares									11,648	12,169	12,801
Weighted average shares - diluted (in shares)									116,367	115,230	113,413
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic (in USD per shares)	$ 2.41	$ 2.53	$ 1.88	$ 1.74	$ 1.49	$ 2.04	$ 1.89	$ 0.74	$ 8.55	$ 6.17	$ 3.36
Net income per share - diluted (in USD per shares)	$ 2.19	$ 2.27	$ 1.69	$ 1.59	$ 1.34	$ 1.82	$ 1.69	$ 0.66	$ 7.70	$ 5.52	$ 2.98
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares									8,041	1,343	1,470
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares									19	0	0
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares									0	994	4,247