Benefit Plans - Defined Benefit Plans - Components of Pension 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
Supplemental Retirement Plan
Components of net periodic benefit cost:
Service cost	$ 120	$ 123	$ 360	$ 369
Interest cost	190	234	570	701
Amortization of prior service cost		199	100	199
Amortization of net actuarial loss	136	101	408	291
Net periodic benefit cost	446	657	1,438	1,560
Defined Benefit Plan, Assets for Plan Benefits	0		0
Split-Dollar Life Insurance Benefit Plan
Components of net periodic benefit cost:
Interest cost	54	62	164	185	$ 246
Amortization of prior transition obligation	(1)	(15)	(3)	(45)
Net periodic benefit cost	$ 53	$ 47	$ 161	$ 140