Note 16 - Stock-Based Compensation - Stock Option Plans (Details) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Outstanding, shares (in shares)	426,913	469,572	513,554
Outstanding, Weighted average exercise price (in dollars per share)	$ 20.14	$ 18.52	$ 17.13
Granted, shares (in shares)	23,350	20,200	16,315
Granted, Weighted average exercise price (in dollars per share)	$ 39.12	$ 36.00	$ 44.02
Exercised, shares (in shares)	(41,650)	(59,393)	(60,127)
Exercised, Weighted average exercise price (in dollars per share)	$ 10.67	$ 12.11	$ 13.56
Forfeited, shares (in shares)	(850)	(3,466)	(170)
Forfeited, Weighted average exercise price (in dollars per share)	$ 19.94	$ 31.59	$ 16.81
Outstanding, shares (in shares)	407,763	426,913	469,572
Outstanding, Weighted average exercise price (in dollars per share)	$ 22.24	$ 20.14	$ 18.52
Exercisable, , shares (in shares)	354,899	365,084	358,270
Weighted-average grant date fair value (in dollars per share)	$ 10.07	$ 11.29	$ 14.68

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Number of options outstanding, including both vested and non-vested options.

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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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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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