Retirement Plans - Reconciliation of Benefit Obligation, Plan Assets, and Funded Status (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets:
Beginning Balance	$ 293,567
Ending Balance	286,539	$ 293,567
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ (165)	$ (165)
Post-Retirement Life Insurance Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.59%	4.10%	4.43%
Retirement Plans
Defined Benefit Plan, Accumulated Benefit Obligation	$ 5,134	$ 4,952
Change in projected benefit obligation:
Beginning Balance	4,952	4,886
Service cost	2	3	$ 5
Interest cost	161	207	204
Actuarial loss (gain)	184	21
Ending Balance	5,134	4,952	4,886
Change in plan assets:
Beginning Balance	0	0
Actual return on assets	0	0
Company contributions	165	165
Foreign exchange impact	0	0
Ending Balance	0	0	$ 0
Funded status (plan assets less projected benefit obligations)	(5,134)	(4,952)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ (165)	$ (165)
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.63%	4.16%	4.43%
Retirement Plans
Defined Benefit Plan, Accumulated Benefit Obligation	$ 228,934	$ 247,276
Change in projected benefit obligation:
Beginning Balance	247,276	256,924
Service cost	0	87	$ 171
Interest cost	8,273	11,024	11,258
Actuarial loss (gain)	12,562	(222)
Foreign exchange impact	0	0
Ending Balance	228,934	247,276	256,924
Change in plan assets:
Beginning Balance	292,044	289,315
Actual return on assets	31,559	23,163
Company contributions	336	103
Foreign exchange impact	0	0
Ending Balance	284,762	292,044	$ 289,315
Funded status (plan assets less projected benefit obligations)	55,828	44,768
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ (39,177)	$ (20,537)
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.38%	1.13%	1.63%
Retirement Plans
Defined Benefit Plan, Accumulated Benefit Obligation	$ 2,535	$ 2,295
Change in projected benefit obligation:
Beginning Balance	2,866	2,796
Service cost	48	51	$ 63
Interest cost	34	46	465
Actuarial loss (gain)	164	229
Foreign exchange impact	238	33
Ending Balance	3,140	2,866	2,796
Change in plan assets:
Beginning Balance	1,523	1,480
Actual return on assets	17	11
Company contributions	319	303
Foreign exchange impact	128	18
Ending Balance	1,777	1,523	$ 1,480
Funded status (plan assets less projected benefit obligations)	(1,363)	(1,343)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ (210)	$ (289)