Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Components of net periodic benefit cost [Abstract]
Contribution made to pension and postretirement plans	$ 0
Pension Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	11	$ 15
Interest cost	329	337
Expected return on plan assets	(686)	(644)
Amortization of net loss (gain)	23	87
Amortization of prior service cost	0	0
Net periodic benefit	(323)	(205)
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	28	32
Interest cost	56	61
Expected return on plan assets	(191)	(181)
Amortization of net loss (gain)	(86)	(54)
Amortization of prior service cost	23	23
Net periodic benefit	$ (170)	$ (119)