Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost — benefits earned during the period	$ 147	$ 141	$ 441	$ 423
Interest cost on projected benefit obligation	1,124	1,262	3,370	3,794
Expected return on assets	(1,393)	(1,356)	(4,179)	(4,068)
Amortization of net loss (gain)	451	503	1,354	1,506
Net expense	329	550	986	1,655
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost — benefits earned during the period	2	2	3	4
Interest cost on projected benefit obligation	82	92	246	276
Expected return on assets	0	0	0	0
Amortization of net loss (gain)	(10)	(14)	(30)	(40)
Net expense	$ 74	$ 80	$ 219	$ 240