Note 13 - Stock-based Compensation - Options Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Number of shares outstanding (in shares)	1,346,863
Number of shares outstanding, weighted-average exercise price (in dollars per share)	$ 11.67
Number of shares outstanding, weighted-average remaining contractual life (Year)	2 years 226 days	3 years 94 days
Number of shares outstanding, aggregate intrinsic value	$ 22,267	$ 33,578
Number of shares exercised (in shares)	(187,742)
Number of shares exercised, weighted-average exercise price (in dollars per share)	$ 3.83
Number of shares outstanding (in shares)	1,159,121	1,346,863
Number of shares outstanding, weighted-average exercise price (in dollars per share)	$ 12.94	$ 11.67
Vested and expected to vest in the future (in shares)	1,159,121
Number of shares vested and expected to vest in the future, weighted-average exercise price (in dollars per share)	$ 12.94
Number of shares vested and expected to vest in the future, weighted-average remaining contractual life (Year)	2 years 226 days
Number of shares vested and expected to vest in the future, aggregate intrinsic value	$ 22,267

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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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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 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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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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

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