Employee Benefit Plans - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) hour	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee pretax Roth contribution percentage of salary	70.00%
Employees age of over with one year period	21 years
Employees age minimum period	1 year
Number of service hours | hour	1,000
Employee pretax contribution percentage	100.00%
Employee contribution	1.00%
Employee contribution percentage	3.00%
Employees compensation	50.00%
Total contributed by employee percentage	2.00%
Corporation's matching contribution and related expenses	$ 1,050,000	$ 906,000	$ 810,000
Compensation percentage in excess of specified amount	5.70%
Excess of compensation	$ 138,000
Salary limit	285,000
Recognized profit sharing expense	1,936,000	1,949,000	1,530,000
Obligations of other liabilities	7,007,000	6,333,000
Expenses related employee benefit plans	992,000	724,000	776,000
Obligations under survivor benefit plan	1,433,000	1,330,000
Other liabilities related to survivor benefit plan	$ 253,000	(1,000)	$ 66,000
Employee retirement health care benefits plan	60 years
Minimum service period for participation in benefit plan	30 years
Accumulated benefit obligation	$ 1,828,000	$ 2,030,000
Amortized from accumulated other comprehensive income into net periodic benefit cost	$ 0
Weighted average discount rate net periodic benefit cost	2.59%	3.78%	3.13%
Accrued benefit obligations	1.55%	2.59%	3.78%
Expected costs of benefit	5.00%
Increase in health care trend rates	$ 136,000
Increase service and interest costs	8,000
Decrease in health care trend rates	124,000
Decrease service and interest costs	$ 9,000
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Qualifying dependents age group	60 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Qualifying dependents age group	65 years