Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 24	$ 7
Interest cost on projected benefit obligations	318	455
Expected return on plan assets	(402)	(549)
Amortization of prior service cost	0	0
Amortization of net loss	135	157
Net periodic benefit cost	75	70
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	35	36
Interest cost on projected benefit obligations	51	64
Expected return on plan assets	0	0
Amortization of prior service cost	(6)	(6)
Amortization of net loss	0	0
Net periodic benefit cost	$ 80	$ 94