Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2014
Numerator:
Net income	$ 270,857	$ 158,857	$ 474,700	$ 409,949
Denominator:
Denominator for basic net earnings per share - weighted-average shares outstanding (shares)	130,277	135,055	131,020	136,752
Effect of dilutive employee stock awards (shares)	1,823	2,731	2,050	2,594
Effect of dilutive Convertible Notes (shares)	0	6,999	1,901	5,892
Effect of dilutive warrants (shares)	555	2,783	1,326	1,316
Denominator for net diluted earnings per share - weighted-average shares outstanding (shares)	132,655	147,568	136,297	146,554
Basic earnings per share (in dollars per share)	$ 2.08	$ 1.18	$ 3.62	$ 3.00
Diluted earnings per share (in dollars per share)	$ 2.04	1.08	$ 3.48	$ 2.80
Senior Notes Due 2019 [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stated interest rate percentage	0.50%		0.50%		0.50%
Weighted-average warrant strike price (in USD per share)	$ 94.18	$ 95.25	$ 94.52