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Stock Options (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Apr. 05, 2012
Employee Stock Option [Member]
Stock option details
Shares available for future grants	15,477		800,000
Maximum exercisable period for options granted	10 years
Stock option activity
Options outstanding at the beginning of the period (in shares)	651,127
Less:
Exercise of stock options (in shares)	71,413
Options forfeited (in shares)	5,375
Options outstanding at the end of the period (in shares)	574,339
Options fully vested and exercisable at the end of the period (in shares)	342,257
Stock Options, Weighted average exercise price
Options outstanding at the beginning, weighted average exercise price (in dollars per share)	$ 27.24
Less:
Options exercised, weighted average exercise price (in dollars per share)	21.70
Options forfeited, weighted average exercise price (in dollars per share)	27.85
Options outstanding at the end, weighted average exercise price (in dollars per share)	27.92
Options fully vested and exercisable at the end, weighted average exercise price (in dollars per share)	$ 23.26
Stock Options, Weighted average remaining contractual term (years)
Options outstanding at the end, weighted average remaining contractual term (years)	5 years
Options fully vested and exercisable at the end, weighted average remaining contractual term (years)	3 years 5 months 19 days
Stock Options, Aggregate intrinsic value
Options outstanding at the end, aggregate intrinsic value	$ 10,624,000
Options fully vested and exercisable at the end, aggregate intrinsic value	7,928,000
Stock-based compensation expense	159,000	$ 219,000
Stock-based compensation cost, unrecognized, related to non-vested options	$ 1,095,000
Stock-based compensation cost, unrecognized, related to non-vested options, weighted-average period of recognition	1 year 7 months 6 days
Incentive Stock Options to 10 Percent Shareholders [Member]
Stock option details
Maximum exercisable period for options granted	5 years

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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