Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Retirement Benefits [Abstract]
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	$ 3,002	$ 3,560
Interest cost	2,194	2,129	4,388	4,258
Expected return on plan assets	(4,727)	(4,815)	(9,454)	(9,630)
Amortization of Prior service cost	0	0	0	0
Amortization of Net loss	765	707	1,530	1,414
Net periodic (income) benefit cost	(267)	(199)	(534)	(398)
RIM Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	53	61	106	122
Interest cost	116	111	232	222
Expected return on plan assets	0	0	0	0
Amortization of Prior service cost	0	0	0	0
Amortization of Net loss	61	103	122	206
Net periodic (income) benefit cost	230	275	460	550
Post-retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	172	93	344	186
Interest cost	321	205	642	410
Expected return on plan assets	0	0	0	0
Amortization of Prior service cost	14	(34)	28	(68)
Amortization of Net loss	99	69	198	138
Net periodic (income) benefit cost	$ 606	$ 333	$ 1,212	$ 666