Benefit Plans - Components of net periodic benefit cost (Details) - Modified Retirement Plan - Unfunded plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Components of net periodic benefit cost
Service cost	$ 626	$ 659	$ 588
Interest cost	744	676	795
Amortization of prior service cost	313	469	531
Amortization of net actuarial losses	367	576	326
Net periodic benefit cost	$ 2,050	$ 2,380	$ 2,240