Earnings Per Share (Net Income Per Share Basic And Diluted) (Details) $ / shares in Units, shares in Thousands			3 Months Ended								12 Months Ended
	Feb. 01, 2017 $ / shares	Apr. 30, 2014 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Numerator:
Income from continuing operations | $			$ (283,889,000)	$ 126,720,000	$ 108,829,000	$ 70,325,000	$ 178,575,000	$ 111,737,000	$ 106,289,000	$ 73,254,000	$ 21,985,000	$ 469,855,000	$ 215,133,000
(Loss) income from discontinued operations, net of income taxes | $			0	0	0	(42,704,000)	21,275,000	20,164,000	14,609,000	10,209,000	(42,704,000)	66,257,000	104,228,000
Net (loss) income | $			$ (283,889,000)	$ 126,720,000	$ 108,829,000	$ 27,621,000	$ 199,850,000	$ 131,901,000	$ 120,898,000	$ 83,463,000	$ (20,719,000)	$ 536,112,000	$ 319,361,000
Denominator:
Denominator for basic earnings per share - weighted-average shares outstanding | shares											150,779	155,134	158,874
Effect of dilutive employee stock awards | shares											2,493	1,950	1,488
Effect of dilutive Convertible Notes | shares											2,231	0	0
Denominator for diluted earnings per share - weighted-average shares outstanding | shares											155,503	157,084	160,362
Basic (loss) earnings per share:
Income from continuing operations (USD per share)			$ (1.93)	$ 0.84	$ 0.72	$ 0.46	$ 1.15	$ 0.72	$ 0.69	$ 0.47	$ 0.15	$ 3.03	$ 1.35
(Loss) income from discontinued operations (USD per share)											(0.28)	0.43	0.66
Basic net earnings per share (USD per share)			(1.93)	0.84	0.72	0.18	1.28	0.85	0.78	0.54	(0.13)	3.46	2.01
Diluted (loss) earnings per share:
Income from continuing operations (USD per share)			(1.93)	0.82	0.70	0.44	1.13	0.71	0.68	0.47	0.14	2.99	1.34
(Loss) income from discontinued operations (USD per share)											(0.27)	0.42	0.65
Diluted net earnings per share (USD per share)			(1.93)	$ 0.82	$ 0.70	$ 0.17	$ 1.26	$ 0.84	$ 0.77	$ 0.54	$ (0.13)	$ 3.41	$ 1.99
Anti-dilutive weighted-average shares from stock awards | shares											215	322	2,151
Senior Notes Due 2019
Diluted (loss) earnings per share:
Convertible debt, conversion price (in dollars per share)			$ 90.00								$ 90.00
Principal amount of notes | $		$ 1,000	$ 1,000								$ 1,000
Convertible debt, conversion ratio	0.0139061	0.011111
GetGo, Inc [Member]
Diluted (loss) earnings per share:
Convertible debt, conversion ratio	0.0139061
GetGo, Inc [Member] | Senior Notes Due 2019
Diluted (loss) earnings per share:
Convertible debt, conversion price (in dollars per share)	$ 71.91