Postretirement Benefits - Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Benefit obligation at beginning of year	$ 2,987	$ 2,642
Service cost	61	53	$ 55
Interest cost	87	105	105
Participant contribution	29	29
Actuarial (gains) / losses	(195)	310	(632)
Benefits paid	(182)	(152)
Benefit obligation at end of year	2,787	2,987	$ 2,642
Change in fair value of plan assets:
Employer contribution	153	123
Participant contribution	29	29
Benefits paid	(182)	(152)
Funded status at end of year	$ (2,787)	$ (2,987)