Pension and Other Post-Retirement Benefits - Projected benefit obligations, the plan assets, and the funded status (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Change in benefit obligation
Service costs	$ 368	$ 226
Interest cost	$ 82	$ 79

Amount of cost recognized for passage of time related to defined benefit plan.

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Name:	us-gaap_DefinedBenefitPlanInterestCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration