Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Feb. 01, 2017	Dec. 31, 2014
Numerator:
Income from continuing operations	$ 106,833	$ 108,829	$ 251,092	$ 179,154
Loss from discontinued operations, net of income taxes	0	0	0	(42,704)
Net income	$ 106,833	$ 108,829	$ 251,092	$ 136,450
Denominator:
Denominator for basic net earnings per share - weighted-average shares outstanding (shares)	135,993	151,212	137,614	152,247
Effect of dilutive employee stock awards (shares)	1,940	2,180	2,360	2,815
Effect of dilutive Convertible Notes (shares)	6,023	2,644	5,258	2,177
Effect of dilutive warrants (shares)	1,491	0	477	0
Denominator for net diluted earnings per share - weighted-average shares outstanding (shares)	145,447	156,036	145,709	157,239
Income from continuing operations, basic (in dollars per share)	$ 0.79	$ 0.72	$ 1.82	$ 1.18
(Loss) from discontinued operations, basic (in dollars per share)	0.00	0.00	0.00	(0.28)
Basic earnings per share (in dollars per share)	0.79	0.72	1.82	0.90
Income from continuing operations, diluted (in dollars per share)	0.73	0.70	1.72	1.14
(Loss) from discontinued operations, diluted (in dollars per share)	0.00	0.00	0.00	(0.27)
Diluted earnings per share (in dollars per share)	0.73	$ 0.70	1.72	$ 0.87
GetGo, Inc. [Member]
Denominator:
Convertible debt, conversion price (in dollars per share)					$ 71.91
Senior Notes Due 2019 [Member]
Denominator:
Strike price of warrants (in dollars per share)	$ 95.25		$ 95.25
Stated interest rate percentage						0.50%
Senior Notes Due 2019 [Member] | GetGo, Inc. [Member]
Denominator:
Convertible debt, conversion price (in dollars per share)					$ 71.91