Employee Benefit and Deferred Compensation Plans - Plan Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation
Benefit obligation at beginning of year	$ 28,020,000
Benefit obligation at end of year	28,226,000	$ 28,020,000
Change in fair value of plan assets
Fair value of plan assets at beginning of year	28,585,000
Fair value of plan assets at end of year	30,549,000	28,585,000
Weighted-average assumptions as of December 31
Accelerated benefit payouts	2,073,000
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	28,020,000	24,945,000
Service cost	0	0	$ 0
Interest cost	984,000	1,176,000	1,043,000
Plan participants’ contributions	0	0
Amendments	0	0
Actuarial loss (gain)	3,239,000	3,671,000
Benefits paid	(4,017,000)	(1,772,000)
Benefit obligation at end of year	28,226,000	28,020,000	24,945,000
Change in fair value of plan assets
Fair value of plan assets at beginning of year	28,585,000	25,206,000
Actual return on plan assets	5,981,000	5,151,000
Contribution by employer	0	0
Benefits paid	(4,017,000)	(1,772,000)
Fair value of plan assets at end of year	30,549,000	28,585,000	25,206,000
Funded status at end of year	$ 2,323,000	$ 565,000
Weighted-average assumptions as of December 31
Discount rate used to determine the benefit obligation	2.44%	3.59%
Other Benefits
Change in benefit obligation
Benefit obligation at beginning of year	$ 707,000	$ 881,000
Service cost	6,000	7,000	8,000
Interest cost	13,000	31,000	31,000
Plan participants’ contributions	52,000	60,000
Amendments	486,000	0
Actuarial loss (gain)	21,000	(60,000)
Benefits paid	(266,000)	(212,000)
Benefit obligation at end of year	1,019,000	707,000	$ 881,000
Change in fair value of plan assets
Funded status at end of year	$ (1,019,000)	$ (707,000)
Weighted-average assumptions as of December 31
Discount rate used to determine the benefit obligation	1.77%	2.91%