Shareholders' Equity Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Before-tax amount [Abstract]
Foreign currency translation adjustment	$ 16,293	$ 15,066
Net unrealized gain (loss) on derivative instruments designated as cash flow hedges	1,436	97
Net hedging (gain) loss reclassified into net income	(19)	378
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	420	406
Total other comprehensive income (loss), before tax	18,130	15,947
Tax (provision) benefit [Abstract]
Foreign currency translation adjustment	7	(50)
Net unrealized gain (loss) on derivative instruments designated as cash flow hedges	(253)	(37)
Net hedging (gain) loss reclassified into net income	5	(146)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(6)	(5)
Total other comprehensive income (loss) tax benefit	(247)	(238)
Net-of-tax amount [Abstract]
Foreign currency translation adjustment	16,300	15,016
Net unrealized gain (loss) on derivative instruments designated as cash flow hedges	1,183	60
Net hedging loss (gain) reclassified into net income	(14)	232
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	414	401
Total other comprehensive income (loss), net of tax	$ 17,883	$ 15,709