Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Years of employment benefits are based upon	5 years
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,501	$ 1,780
Interest cost	2,194	2,129
Expected return on plan assets	(4,727)	(4,815)
Amortization of Prior service cost	0	0
Amortization of Net loss	765	707
Net periodic (income) cost	(267)	(199)
RIM Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	53	61
Interest cost	116	111
Expected return on plan assets	0	0
Amortization of Prior service cost	0	0
Amortization of Net loss	61	103
Net periodic (income) cost	230	275
Post-retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	172	187
Interest cost	321	312
Expected return on plan assets	0	0
Amortization of Prior service cost	14	(26)
Amortization of Net loss	99	195
Net periodic (income) cost	$ 606	$ 668