Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year			$ 2,500
Post-Retirement Health Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year			$ 260
Service cost	$ 13	$ 14
Interest cost	43	46
Expected return on plan assets	0	0
Amortization of transition obligation	0	0
Net amortization of prior service cost	0	0
Net amortization of net (gain) loss	0	0
Net Periodic Benefit Cost	56	60
Defined Benefit Plan, Contributions by Employer	55
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	358	470
Interest cost	905	932
Expected return on plan assets	(985)	(857)
Amortization of transition obligation	0	0
Net amortization of prior service cost	0	0
Net amortization of net (gain) loss	301	484
Net Periodic Benefit Cost	579	$ 1,029
Defined Benefit Plan, Contributions by Employer	$ 400