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, 2016	Dec. 31, 2015
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	$ 28,649
Plan assets, ending balance	25,831	$ 28,649
Real Estate Investments [Member] | Measured at net asset value [Domain]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Purchases & settlements	33,442	29,717
Pension Plan [Member]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Plan assets, beginning balance	672,153	719,787
Unrealized gains	7,746
Plan assets, ending balance	715,885	672,153
Pension Plan [Member] | Measured at net asset value [Domain]
Schedule of Level Three Defined Benefit Plan Assets [Roll Forward]
Plan assets, beginning balance	58,366
Plan assets, ending balance	$ 59,273	$ 58,366