Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 37	$ 29
Interest cost on projected benefit obligations	9	95
Expected return on plan assets	0	(244)
Amortization of prior service benefit	0	0
Amortization of net loss	9	88
Net periodic benefit cost (income)	55	(32)
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	29	34
Interest cost on projected benefit obligations	53	48
Expected return on plan assets	0	0
Amortization of prior service benefit	(25)	(6)
Amortization of net loss	0	0
Net periodic benefit cost (income)	$ 57	$ 76