Benefit Plans - Components of net periodic benefit cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Modified Retirement Plan | Unfunded plan
Components of net periodic benefit cost
Service cost	$ 659	$ 588	$ 392
Interest cost	676	795	931
Expected return on plan assets	0	0	0
Amortization of prior service cost	469	531	635
Amortization of net actuarial losses	576	326	59
Net periodic benefit cost	$ 2,380	$ 2,240	2,017
Funded Plan | Funded plan
Components of net periodic benefit cost
Service cost			0
Interest cost			166
Expected return on plan assets			(106)
Amortization of prior service cost			0
Amortization of net actuarial losses			0
Net periodic benefit cost			$ 60