Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 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	$ 26	$ 27
Interest cost	43	46	86	93
Expected return on plan assets	0	0	0	0
Amortization of transition obligation	0	0	0	0
Net amortization of prior service cost	0	0	0	0
Net amortization of net (gain) loss	0	0	0	0
Net Periodic Benefit Cost	56	60	112	120
Defined Benefit Plan, Plan Assets, Contributions by Employer			111
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	358	470	716	941
Interest cost	905	932	1,810	1,865
Expected return on plan assets	(985)	(857)	(1,970)	(1,715)
Amortization of transition obligation	0	0	0	0
Net amortization of prior service cost	0	0	0	0
Net amortization of net (gain) loss	301	484	602	967
Net Periodic Benefit Cost	$ 579	$ 1,029	1,158	$ 2,058
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 977