Net Investment Hedge Net Investment Hedge (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency translation gain (loss), net of $1.2 million, $1.3 million, and $1.8 million tax, respectively	$ (65,046)	$ 18,687	$ (20,842)
Senior Subordinated Notes [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency translation gain (loss), net of $1.2 million, $1.3 million, and $1.8 million tax, respectively	$ (56,200)	$ 13,000