Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 13	$ 38	$ 39	$ 74
Interest cost on projected benefit obligations	2	8	6	18
Amortization of net loss (benefit)	2	9	4	18
Net periodic benefit cost	17	55	49	110
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	15	25	77	52
Interest cost on projected benefit obligations	34	53	116	105
Amortization of net loss (benefit)	(17)	(29)	(17)	(59)
Net periodic benefit cost	$ 32	$ 49	$ 176	$ 98