Pension Plans and Postretirement Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Net periodic benefit cost for pension plans and the postretirement benefit plan
Service Cost	$ 0	$ 0	$ 0	$ 0
Interest Cost	1,041	1,161	3,123	3,483
Expected Return on Plan Assets	(1,281)	(1,238)	(3,845)	(3,714)
Amortization of Prior Service Credit	0	0	0	0
Amortization of Net Actuarial Losses (Gains)	498	433	1,494	1,298
Net Periodic Benefit Cost	258	356	772	1,067
Employer Contributions	200		400
Estimated Future Employer Contributions in Current Fiscal Year	500		500
Postretirement Benefits
Net periodic benefit cost for pension plans and the postretirement benefit plan
Service Cost	114	123	344	369
Interest Cost	235	272	706	816
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credit	(142)	(81)	(426)	(242)
Amortization of Net Actuarial Losses (Gains)	(61)	(111)	(185)	(331)
Net Periodic Benefit Cost	146	$ 203	439	$ 612
Employer Contributions	300		800
Estimated Future Employer Contributions in Current Fiscal Year	$ 900		$ 900