Benefit Plans - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension and Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Net Actuarial (Gain)/Loss	$ 95,636	$ 93,243
Net Prior Service Cost/(Credit)	(2,989)	(3,853)
Net Transition Obligation/(Asset)	0	0
Total at Year End	92,647	89,390	$ 45,143
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Net Actuarial (Gain)/Loss	(5,311)	(8,222)
Net Prior Service Cost/(Credit)	(18,640)	(25,289)
Net Transition Obligation/(Asset)	0	0
Total at Year End	$ (23,951)	$ (33,511)	$ (41,377)