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, 2018	Dec. 31, 2017
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		$ 27,197
Plan assets, ending balance	$ 4,599
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	681,573	715,885
Unrealized gains	15,528
Plan assets, ending balance	625,646	681,573
Pension Plan [Member] | Measured at net asset value [Domain]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Plan assets, beginning balance	27,197
Plan assets, ending balance	$ 4,599	$ 27,197