Retirement Plans - Components of Prepaid (Accrued) Cost (Details 3) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Retirement Plans
Prepaid pension asset	$ 57,050	$ 46,183
Post-Retirement Life Insurance Plan
Retirement Plans
Accrued expenses and other liabilities	(418)	(387)
Long-term pension obligations	(4,716)	(4,565)
Components of prepaid (accrued) cost, net	(5,134)	(4,952)
Domestic Plan [Member]
Retirement Plans
Prepaid pension asset	57,050	46,183
Accrued expenses and other liabilities	(100)	(317)
Long-term pension obligations	(1,122)	(1,098)
Components of prepaid (accrued) cost, net	55,828	44,768
Foreign Plan [Member]
Retirement Plans
Prepaid pension asset	0	0
Accrued expenses and other liabilities	0	0
Long-term pension obligations	(1,363)	(1,343)
Components of prepaid (accrued) cost, net	$ (1,363)	$ (1,343)