Earnings Per Share (Details) $ / shares in Units, shares in Thousands, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 01, 2017 $ / shares	Jan. 31, 2017 $ / shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares
Numerator:
Income from continuing operations | $			$ 126,720	$ 111,737	$ 305,874	$ 291,280
Income (loss) from discontinued operations, net of income taxes | $			0	20,164	(42,704)	44,982
Net income | $			$ 126,720	$ 131,901	$ 263,170	$ 336,262
Denominator:
Denominator for basic net earnings per share - weighted-average shares outstanding (shares) | shares			151,156	155,525	151,896	154,847
Effect of dilutive employee stock awards (shares) | shares			1,987	2,007	2,538	1,850
Effect of dilutive Convertible Notes (shares) | shares			1,484	0	1,950	0
Denominator for net diluted earnings per share - weighted-average shares outstanding (shares) | shares			154,627	157,532	156,384	156,697
Income from continuing operations, basic (in dollars per share)			$ 0.84	$ 0.72	$ 2.01	$ 1.88
Income (loss) from discontinued operations, basic (in dollars per share)			0.00	0.13	(0.28)	0.29
Basic earnings per share (in dollars per share)			0.84	0.85	1.73	2.17
Income from continuing operations, diluted (in dollars per share)			0.82	0.71	1.96	1.86
Income (loss) from discontinued operations, diluted (in dollars per share)			0.00	0.13	(0.28)	0.29
Diluted earnings per share (in dollars per share)			$ 0.82	$ 0.84	$ 1.68	$ 2.15
Anti-dilutive weighted-average shares from stock awards (shares) | shares			393	60	225	460
Senior Notes Due 2019 [Member]
Denominator:
Convertible debt, conversion price (in dollars per share)	$ 71.91	$ 90
Convertible debt, conversion ratio	0.0139061	0.011111
GetGo, Inc. [Member]
Denominator:
Convertible debt, conversion price (in dollars per share)	$ 71.91
Convertible debt, conversion ratio	0.0139061