New Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax benefit related to the settlement of share-based awards during period	$ 5,100
Net cash provided by (used in) operating activities of continuing operations	372,475	$ 390,187	$ 628,649
Net cash provided (used in) financing activities of continuing operations	227,764	(133,836)	(1,227,844)
Cumulative adjustment to retained earnings (less than)	(2,191,059)	(1,876,081)
Accounting Standards Update 2016-09, Statutory Tax Withholding Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities of continuing operations		8,300	9,800
Net cash provided (used in) financing activities of continuing operations		(8,300)	(9,800)
Accounting Standards Update 2016-09, Excess Tax Benefit Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities of continuing operations		700	700
Net cash provided (used in) financing activities of continuing operations		$ (700)	$ (700)
Pro Forma | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment to retained earnings (less than)	$ 10,000