Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year					$ 2,300
Post-Retirement Health Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year					$ 240
Service cost	$ 11	$ 9	$ 22	$ 19
Interest cost	25	31	51	62
Expected return on plan assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	0	0	0
Net amortization of net (gain) loss	0	0	0	0
Net Periodic Benefit Cost	36	40	73	81
Defined Benefit Plan, Plan Assets, Contributions by Employer			111
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	338	325	677	650
Interest cost	658	779	1,316	1,558
Expected return on plan assets	(1,179)	(1,049)	(2,357)	(2,099)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	0	0	0
Net amortization of net (gain) loss	518	492	1,036	984
Net Periodic Benefit Cost	$ 335	$ 547	672	$ 1,093
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 574