Stock Option Plans - Narrative (Details) - USD ($)		3 Months Ended
Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation (in shares)	115,388	2,947
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares)		910	11,745
Stock option expense		$ 294,500
Future expense	$ 1,300,000	1,300,000
Exercised		$ 0	$ 85,268
Closing share price (in usd per share)	$ 40.11	$ 40.11
Share-based compensation arrangement by share-based payment award, options, grants since inception	1,407,625	1,407,625
Weighted average remaining contractual life of the Company's outstanding options		6 years 2 months 12 days
Weighted average remaining contractual life of the Company's exercisable options		5 years 2 months 12 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)		6,187
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		10 years
Employee Stock Option \| Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants Since Inception

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Number of shares issued pursuant to the terms of a deferred compensation arrangement.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Price of a single share of a number of saleable stocks of a company.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).

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