Pension and Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 918	$ 670
Defined Benefit Plan, Interest Cost	1,008	1,111
Defined Benefit Plan, Expected Return on Plan Assets	(1,326)	(1,344)
Defined Benefit Plan, Amortization of Losses	869	808
Defined Benefit Plan, Amortization of Prior Service Cost	(23)	(25)
Defined Benefit Plan, Net Periodic Benefit Cost	1,446	1,220
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	7,800
Defined Benefit Plan, Contributions by Employer	3,400
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	3	4
Defined Benefit Plan, Interest Cost	33	39
Defined Benefit Plan, Expected Return on Plan Assets	0	0
Defined Benefit Plan, Amortization of Losses	5	15
Defined Benefit Plan, Amortization of Prior Service Cost	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	41	$ 58
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	500
Defined Benefit Plan, Contributions by Employer	$ 200