Postretirement Benefits - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Service cost-benefits attributable to service during the period	$ 61	$ 53	$ 55
Interest cost on accumulated postretirement benefit obligation	87	105	105
Net amortization and deferral	13	14	18
Net periodic postretirement benefit cost	161	172	178
Actuarial (gains) / losses	(195)	310	(632)
Plan amendment for acquisition			72
Amortization of prior service cost and actuarial losses	(13)	(14)	(18)
Total recognized in comprehensive income (loss)	(208)	296	(578)
Total recognized in net periodic postretirement benefit cost and other comprehensive income	$ (47)	$ 468	$ (400)