Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost — benefits earned during the period	$ 137	$ 133	$ 274	$ 265
Interest cost on projected benefit obligation	1,355	1,280	2,710	2,598
Expected return on assets	(1,519)	(1,888)	(3,038)	(3,813)
Settlement loss	0	1,607	0	1,607
Amortization of net loss (gain)	464	278	928	569
Net expense	437	1,410	874	1,226
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost — benefits earned during the period	1	2	2	4
Interest cost on projected benefit obligation	97	93	194	185
Expected return on assets	0	0	0	0
Settlement loss	0	0	0	0
Amortization of net loss (gain)	(19)	(24)	(38)	(48)
Net expense	$ 79	$ 71	$ 158	$ 141