Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Components of Net Periodic Benefit Cost
Service cost	$ 351	$ 313	$ 1,053	$ 940	$ 1,254
Interest cost	319	326	956	979	$ 1,306
Net loss	197	135	591	405
Net periodic pension cost	$ 867	$ 774	$ 2,600	$ 2,324