Note 11 - Share Option and Equity Incentive Plan - Stock Option Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of share options outstanding (in shares)	3,104,613
Number of share options outstanding, weighted average exercise price (in dollars per share)	$ 11.62
Number of share options granted (in shares)	796,264
Weighted-average exercise price ($) (in dollars per share)	$ 13.37
Number of share options exercised (in shares)	(694,322)	(500,182)	(85,943)
Number of share options exercised, weighted average exercise price (in dollars per share)	$ 4.67
Number of share options forfeited (in shares)	(643,386)
Number of share options forfeited, weighted average exercise price (in dollars per share)	$ 14.31
Number of share options oustanding (in shares)	2,563,169	3,104,613
Number of share options oustanding, weighted average exercise price (in dollars per share)	$ 13.37	$ 11.62
Number of share options vested or expected to vest (in shares)	2,494,307
Number of share options vested or expected to vest, weighted average exercise price (in dollars per share)	$ 13.37
Number of share options exercisable (in shares)	1,401,639
Number of share options exercisable, weighted average exercise price (in dollars per share)	$ 13.47

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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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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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 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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