Pension and Postretirement Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 237	$ 200	$ 441	$ 365
Defined Benefit Plan, Interest Cost	359	347	684	659
Defined Benefit Plan, Amortization of Gain (Loss)	509	698	850	1,158
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	1,105	1,245	1,975	2,182
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	7	13	14	25
Defined Benefit Plan, Interest Cost	48	54	98	109
Defined Benefit Plan, Amortization of Gain (Loss)	2	11	3	23
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 57	$ 78	$ 115	$ 157