Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost — benefits earned during the period	$ 141	$ 137	$ 282	$ 274
Interest cost on projected benefit obligation	1,266	1,355	2,530	2,710
Expected return on assets	(1,356)	(1,519)	(2,712)	(3,038)
Amortization of net loss (gain)	502	464	1,004	928
Net expense	553	437	1,104	874
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost — benefits earned during the period	1	1	3	2
Interest cost on projected benefit obligation	92	97	184	194
Expected return on assets	0	0	0	0
Amortization of net loss (gain)	(13)	(19)	(27)	(38)
Net expense	$ 80	$ 79	$ 160	$ 158