Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	$ 15	33	$ 46
Interest cost	326	343	977	1,029
Expected return on plan assets	(686)	(669)	(2,058)	(1,994)
Amortization of net loss (gain)	17	46	50	138
Amortization of prior service cost	0	0	0	0
Net periodic benefit	(332)	(265)	(998)	(781)
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	26	32	77	96
Interest cost	54	61	164	184
Expected return on plan assets	(190)	(180)	(571)	(540)
Amortization of net loss (gain)	(89)	(54)	(258)	(163)
Amortization of prior service cost	23	22	68	67
Net periodic benefit	$ (176)	$ (119)	$ (520)	$ (356)