Derivative Financial Instruments Effect of Net Investment Hedge Nonderivative Financial Instrument on OCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	$ (229,327)
Unrealized gain (loss) on derivative instruments	360	$ (1,087)	$ 76
Realized (gains) losses reclassified into net income (loss)	563	812	1,010
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(170,478)	(229,327)
Accumulated Net Gain (Loss) from Derivative and Nonderivative Instruments Designated as Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(14,337)	(14,062)	(15,148)
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	$ (13,414)	$ (14,337)	$ (14,062)