Note 6 - Share-based Compensation - Stock Option Transactions (Details) - $ / shares	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Outstanding options (in shares)			633,877
Outstanding options (in dollars per share)			$ 13.33
Granted options (in shares)	43,245	53,970	141,630	155,142
Granted options (in dollars per share)			$ 22.20
Exercised options (in shares)			(60,058)
Exercised options (in dollars per share)			$ 10.08
Lapsed options (in shares)			(1,800)
Lapsed options (in dollars per share)			$ 5.88
Cancelled options (in shares)			(2,620)
Cancelled options (in dollars per share)			$ 20.05
Outstanding options (in shares)	711,029		711,029
Outstanding options (in dollars per share)	$ 15.36		$ 15.36

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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