Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 27	$ 8	$ 82	$ 22
Interest cost on projected benefit obligations	453	450	1,358	1,350
Expected return on plan assets	(544)	(538)	(1,630)	(1,614)
Amortization of prior service cost	0	0	0	0
Amortization of net loss	156	177	466	532
Settlement expense	740	0	740	0
Net periodic benefit cost	832	97	1,016	290
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	34	36	103	110
Interest cost on projected benefit obligations	64	62	193	188
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(6)	14	(19)	40
Amortization of net loss	0	0	0	0
Settlement expense	0	0	0	0
Net periodic benefit cost	$ 92	$ 112	$ 277	$ 338