Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 13	$ 37
Interest cost on projected benefit obligations	2	10
Amortization of net loss (benefit)	1	9
Net periodic benefit cost	16	56
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	31	29
Interest cost on projected benefit obligations	41	53
Amortization of net loss (benefit)	0	(25)
Net periodic benefit cost	$ 72	$ 57