Pension and Other Post-Retirement Benefits - Benefit costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Service costs	$ 1,441	$ 1,136	$ 870
Interest cost	323	292	311
Expected return on plan assets	(199)	(178)	(157)
Amortization of actuarial gains	(19)	(46)	(76)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	(91)	(499)	7
Net periodic benefit cost	$ 1,455	$ 705	$ 955