Note 10 - Share Option and Equity Incentive Plans (Details Textual) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Share-based Payment Arrangement, Expense	$ 845,000	$ 1,824,000
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense	649,000	985,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 4,100,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years
Restricted Stock and Restricted Stock Units (RSU's) [Member]
Share-based Payment Arrangement, Expense	$ 196,000	$ 839,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 2,400,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years
2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	5,000
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 14.59
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 6.77
2013 Plan [Member] \| Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
2013 Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	0
2013 Plan [Member] \| Restricted Stock Units (RSUs) [Member] \| Second Anniversary of Grant Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	40.00%
2013 Plan [Member] \| Restricted Stock Units (RSUs) [Member] \| Third Anniversary of Grant Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	30.00%
2013 Plan [Member] \| Restricted Stock Units (RSUs) [Member] \| Fourth Anniversary of Grant Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	30.00%

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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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Percentage of vesting of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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