Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 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	$ 16	22	$ 31
Interest cost	322	349	651	686
Expected return on plan assets	(686)	(681)	(1,372)	(1,325)
Amortization of net loss (gain)	10	5	33	92
Amortization of prior service cost	0	0	0	0
Net periodic benefit	(343)	(311)	(666)	(516)
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	23	32	51	64
Interest cost	54	61	110	123
Expected return on plan assets	(190)	(180)	(381)	(360)
Amortization of net loss (gain)	(83)	(55)	(169)	(109)
Amortization of prior service cost	22	22	45	45
Net periodic benefit	$ (174)	$ (120)	$ (344)	$ (237)