Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 13	$ 37	$ 26	$ 74
Interest cost on projected benefit obligations	2	9	4	18
Amortization of net loss (benefit)	1	9	2	18
Net periodic benefit cost	16	55	32	110
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	31	23	62	52
Interest cost on projected benefit obligations	41	51	82	105
Amortization of net loss (benefit)	0	(34)	0	(59)
Net periodic benefit cost	$ 72	$ 40	$ 144	$ 98