Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2014
Numerator:
Net income	$ 110,348	$ 144,259
Denominator:
Denominator for basic net earnings per share - weighted-average shares outstanding (shares)	131,483	139,248
Effect of dilutive employee stock awards (shares)	2,834	2,780
Effect of dilutive Convertible Notes (shares)	5,016	4,360
Effect of dilutive warrants (shares)	1,692	0
Denominator for net diluted earnings per share - weighted-average shares outstanding (shares)	141,025	146,388
Basic earnings per share (in dollars per share)	$ 0.84	$ 1.04
Diluted earnings per share (in dollars per share)	$ 0.78	$ 0.99
Senior Notes Due 2019 [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stated interest rate percentage	0.50%		0.50%
Denominator:
Strike price of warrants (in dollars per share)	$ 94.62
Convertible debt, conversion price (in dollars per share)	$ 71.44