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Stock Option Plans - Narrative (Details) - USD ($)			3 Months Ended				6 Months Ended
Stock Option Plans - Narrative (Details) - USD ($)	Apr. 24, 2020	Sep. 30, 2019	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation (in shares)		112,491					4,920
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares)			11,745	11,745	48,772	485
Stock option expense							$ 700,700
Future expense			$ 2,200,000				$ 2,200,000
Closing share price (in usd per share)			$ 32.27				$ 32.27
Granted (in shares)							238,000
Weighted average remaining contractual life of the Company's outstanding options							6 years 3 months 18 days
Weighted average remaining contractual life of the Company's exercisable options							4 years 3 months 18 days
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares)							6,837
Directors and Certain Officers
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	238,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period							10 years
Employee Stock Option \| Officers
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period							4 years
Additional Compensation Plan \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for annual award (in shares)	200