Pension Plans and Postretirement Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefits
Net periodic benefit cost for pension plans and the postretirement benefit plan
Service Cost	$ 0	$ 0	$ 0	$ 0
Interest Cost	1,161	1,209	2,322	2,418
Expected Return on Plan Assets	(1,238)	(1,281)	(2,476)	(2,562)
Amortization of Prior Service Credit	0	0	0	0
Amortization of Net Actuarial Losses (Gains)	432	388	865	777
Net Periodic Benefit Cost	355	316	711	633
Employer Contributions	100		200
Estimated Future Employer Contributions in Current Fiscal Year			10,500
Postretirement Benefits
Net periodic benefit cost for pension plans and the postretirement benefit plan
Service Cost	123	137	246	274
Interest Cost	272	294	544	588
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credit	(80)	(80)	(161)	(161)
Amortization of Net Actuarial Losses (Gains)	(110)	(76)	(220)	(151)
Net Periodic Benefit Cost	205	$ 275	409	$ 550
Employer Contributions	$ 300		500
Estimated Future Employer Contributions in Current Fiscal Year			$ 1,000