Retirement Plans (Schedule of Benefit Obligation, Fair Value of Assets, and Funded Status of the Plans) (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
UNITED STATES
Changes in benefit obligation:
Benefit obligation at beginning of year	$ 18,241	$ 17,759
Service cost	0	36	$ 38
Interest cost	684	746	742
Actuarial loss	775	534
Benefits paid	(917)	(834)
Benefit obligation at end of year	18,783	18,241	17,759
Change to plan assets:
Fair value of assets at beginning of year	14,180	14,235
Actual gain on plan assets	1,629	779
Benefits paid	(917)	(834)
Fair value of assets at end of year	14,892	14,180	14,235
Funded status at end of year	(3,891)	(4,061)
Amounts recognized in the consolidated balance sheet consist of:
Other long-term liabilities	(3,891)	(4,061)
Amounts recognized in accumulated other comprehensive income consist of:
Net loss	3,913	4,186
Foreign Plan
Changes in benefit obligation:
Benefit obligation at beginning of year	8,104	7,862
Interest cost	236	259	295
Actuarial loss	(451)	1,532
Benefits paid	(322)	(273)
Foreign currency exchange rate changes	768	(1,276)
Benefit obligation at end of year	8,335	8,104	7,862
Change to plan assets:
Fair value of assets at beginning of year	5,826	6,661
Actual gain on plan assets	573	265
Employer contribution	276	253
Benefits paid	(322)	(273)
Foreign currency exchange rate changes	551	(1,080)
Fair value of assets at end of year	6,904	5,826	$ 6,661
Funded status at end of year	(1,431)	(2,278)
Amounts recognized in the consolidated balance sheet consist of:
Other long-term liabilities	(1,431)	(2,278)
Amounts recognized in accumulated other comprehensive income consist of:
Net loss	1,161	2,015
Prior service cost	39	53
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax, Total	$ 1,200	$ 2,068