Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Feb. 01, 2017	Dec. 31, 2014
Numerator:
Income from continuing operations	$ 144,259	$ 70,325
Loss from discontinued operations, net of income taxes	0	(42,704)
Net income	$ 144,259	$ 27,621
Denominator:
Denominator for basic net earnings per share - weighted-average shares outstanding (shares)	139,248	153,247
Effect of dilutive employee stock awards (shares)	2,780	3,446
Effect of dilutive Convertible Notes (shares)	4,360	1,676
Denominator for net diluted earnings per share - weighted-average shares outstanding (shares)	146,388	158,369
Income from continuing operations, basic (in dollars per share)	$ 1.04	$ 0.46
(Loss) from discontinued operations, basic (in dollars per share)	0.00	(0.28)
Basic earnings per share (in dollars per share)	1.04	0.18
Income from continuing operations, diluted (in dollars per share)	0.99	0.44
(Loss) from discontinued operations, diluted (in dollars per share)	0.00	(0.27)
Diluted earnings per share (in dollars per share)	$ 0.99	$ 0.17
Anti-dilutive weighted-average shares from stock awards (shares)	84	54
GetGo, Inc. [Member]
Denominator:
Convertible debt, conversion price (in dollars per share)			$ 71.91
Senior Notes Due 2019 [Member]
Denominator:
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