Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Term of Insurance Contracts to Fund Benefits	5 years
Deferred Compensation Arrangement with Individual, Employer Contribution	$ 100	$ 200	$ 300
Deferred Compensation Arrangement with Individual, Compensation Expense	1,400	1,200	1,700
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	$ (77)	$ (81)	(85)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.00%	1.90%
Defined Benefit Plan, Benefit Obligation	$ 63,398	$ 56,082	50,759
Defined Benefit Plan, Service Cost	1,494	1,456	1,787
Defined Benefit Plan, Interest Cost	1,121	1,329	1,192
Defined Benefit Plan, Benefits Paid	(1,212)	(1,139)
defined benefit plan, Administrative Expenses	(35)	(31)
Defined Benefit Plan, Actuarial Net (Gains) Losses	(1,005)	5,225
Defined Benefit Plan, Foreign Currency Exchange Rate Changes, Benefit Obligation	6,953	(1,517)
Defined Benefit Plan, Future Amortization of Gain (Loss)	(300)
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0	0	(96)
Defined Benefit Plan, Foreign Currency Exchange Rate Changes, Plan Assets	5,744	(1,258)
Defined Benefit Plan, Fair Value of Plan Assets	53,145	46,134	$ 41,116
Defined Benefit Plan, Actual Return on Plan Assets	919	6,328
Defined Benefit Plan, Contributions by Employer	1,595	1,118
Defined Benefit Plan, Funded Status of Plan	(10,253)	(9,948)
Defined Benefit Plan, Accumulated Benefit Obligation	56,035	47,980
Interest Rate Swap [Domain]
Defined Benefit Plan Disclosure [Line Items]
Interest Rate Derivatives, at Fair Value, Net	$ (191)	$ (659)