Note 7 - Stock-based Compensation (Details Textual) - USD ($)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement, Expense	$ 78,000	$ 50,000
Share-based Payment Arrangement, Expense, Tax Benefit	6,000	3,000
Proceeds from Stock Options Exercised	35,000	76,000
Share-based Payment Arrangement, Exercise of Option, Tax Benefit	$ 10,000	$ 0
Stock Option Plan 2013 [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)	396,835
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)	101,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	5,000	0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 768,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	3 years 73 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	$ 189,000	$ 197,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 235,000	$ 251,000
Stock Option Plan 2013 [Member] \| Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years

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

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Aggregate number of common shares reserved for future issuance.

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