Note 11 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Options outstanding, number of options (in shares)	1,515,461
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.11
Options outstanding, weighted average remaining contract term (Year)	5 years 164 days	6 years 208 days
Options outstanding, aggregate intrinsic value	$ 4,793	$ 22,125
Granted, number of options (in shares)
Granted, weighted average exercise price (in dollars per share)
Exercised, number of options (in shares)	(70,288)
Exercised, weighted average exercise price (in dollars per share)	$ 9.74
Canceled or forfeited, number of options (in shares)	(62,187)
Canceled or forfeited, weighted average exercise price (in dollars per share)	$ 8.65
Options outstanding, number of options (in shares)	1,382,986	1,515,461
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.10	$ 9.11
Exercisable, number of options (in shares)	1,192,671
Exercisable, weighted average exercise price (in dollars per share)	$ 8.46
Exercisable, weighted average remaining contract term (Year)	5 years 69 days
Exercisable, aggregate intrinsic value	$ 4,527

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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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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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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