New Accounting Pronouncements Impact of new accounting pronouncement (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts Receivable, Net, Current	$ 462,619	$ 489,445	$ 494,049
Other Assets, Current	86,547	$ 105,382	$ 100,778
Accounts Receivable [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance without adoption of ASC 606	465,468
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(2,849)
Other Current Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance without adoption of ASC 606	83,698
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 2,849