Retirement Plans (Income (Loss) Estimated to be Amortized from Accumulated Other Comprehensive Income (Loss) into Net Periodic Cost) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	$ 0
Net gain (loss)	(1,398)
Total	(1,398)
Pension Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	0
Net gain (loss)	(1,436)
Total	(1,436)
Postretirement Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	0
Net gain (loss)	105
Total	105
Supplemental Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	0
Net gain (loss)	(67)
Total	$ (67)