Note 12 - Share-based Compensation - Stock Option Transactions (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Outstanding Options (in shares)	633,877	825,251
Outstanding options (in dollars per share)	$ 13.33	$ 10.46
Granted (in shares)	141,630	155,142	172,862
Granted (in dollars per share)	$ 22.20	$ 18.67
Exercised (in shares)	(94,241)	(336,726)
Exercised (in dollars per share)	$ 9.56	$ 8.71
Lapsed (in shares)	(1,800)	(1,100)
Lapsed (in dollars per share)	$ 5.88	$ 5.86
Cancelled (in shares)	(2,620)	(8,690)
Cancelled (in dollars per share)	$ 20.05	$ 15.82
Outstanding Options (in shares)	676,846	633,877	825,251
Outstanding Options (in dollars per share)	$ 15.70	$ 13.33	$ 10.46

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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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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 of the plan that expired.

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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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Number of share options (or share units) exercised during the current period.

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