Pension and Other Post-Retirement Benefit Plans (Fair Value Measurements Using Significant Level 3 Unobservable Inputs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Hedge Funds & Private Equity [Member] | Measured at net asset value [Domain]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Plan assets, beginning balance	$ 2,083
Plan assets, ending balance	403	$ 2,083
Real Estate Investments [Member] | Measured at net asset value [Domain]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Purchases & settlements	0	0
Pension Plan [Member]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Plan assets, beginning balance	746,763	625,646
Unrealized gains	7,100
Plan assets, ending balance	843,895	746,763
Pension Plan [Member] | Measured at net asset value [Domain]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Plan assets, beginning balance	2,083
Plan assets, ending balance	$ 403	$ 2,083