Recent Accounting Pronouncements (Changes in Condensed Consolidated Statements of Cash Flow) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities					$ 336,950	$ 339,625
Net cash used in financing activities					$ (290,399)	$ (347,726)
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	$ 129,014	$ 125,395	$ 128,471	$ 85,979
Net cash used in financing activities	(137,408)	(89,378)	(162,861)	(95,707)
Accounting Standards Update 2016-09 | Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	128,954	125,464	128,384	85,777
Net cash used in financing activities	(137,348)	(89,447)	(162,774)	(95,505)
Accounting Standards Update 2016-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	60	(69)	87	202
Net cash used in financing activities	$ (60)	$ 69	$ (87)	$ (202)