Note 9 - Share-based Compensation - Stock Option Activity (Details) - $ / shares	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Options outstanding at beginning of year (in shares)	624,256
Options outstanding at beginning of year (in dollars per share)	$ 8.87
Number of shares, granted (in shares)
Weighted average exercise price, granted (in dollars per share)
Number of shares, exercised (in shares)
Weighted average exercise price, exercised (in dollars per share)
Number of shares, forfeited prior to vesting (in shares)
Weighted average exercise price, forfeited prior to vesting (in dollars per share)
Number of shares, canceled or expired (in shares)	(53,733)
Weighted average exercise price, canceled or expired (in dollars per share)	$ 9.49
Options outstanding at March 31, 2019 (in shares)	570,523	624,256
Options outstanding at March 31, 2019 (in dollars per share)	$ 8.81	$ 8.87
Options exercisable at end of March 31, 2019 (in shares)	514,438
Options exercisable at end of March 31, 2019 (in dollars per share)	$ 8.63

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 weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, 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 or that expired.

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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 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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