Employee Benefits - Schedule of Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Net periodic benefit cost for pension plans and the postretirement benefit plan
Service Cost	$ 0	$ 0	$ 0
Interest Cost	3,627	4,401	4,193
Expected Return on Plan Assets	(5,028)	(4,993)	(5,122)
Amortization of Prior Service Credit	0	0	0
Amortization of Net Actuarial Losses (Gains)	2,318	1,937	2,099
Net Periodic Benefit Cost	917	1,345	1,170
Postretirement Benefits
Net periodic benefit cost for pension plans and the postretirement benefit plan
Service Cost	578	455	457
Interest Cost	945	1,025	936
Expected Return on Plan Assets	0	0	0
Amortization of Prior Service Credit	(246)	(288)	(567)
Amortization of Net Actuarial Losses (Gains)		(339)	(264)
Net Periodic Benefit Cost	$ 1,277	$ 853	$ 562