Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
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	$ 8	$ 11	25	$ 33
Interest cost	299	326	898	977
Expected return on plan assets	(753)	(686)	(2,259)	(2,058)
Amortization of net (gain) loss	0	17	0	50
Amortization of prior service cost	0	0	0	0
Net periodic benefit	(446)	(332)	(1,336)	(998)
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	26	52	77
Interest cost	47	54	156	164
Expected return on plan assets	(323)	(190)	(704)	(571)
Amortization of net (gain) loss	(189)	(89)	(367)	(258)
Amortization of prior service cost	(73)	23	(28)	68
Net periodic benefit	$ (538)	$ (176)	$ (891)	$ (520)