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Note 10 - Share Option and Equity Incentive Plan (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 5,100,000		$ 5,100,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition			2 years 219 days
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense	658,000	$ 748,000	$ 1,900,000	$ 2,400,000
Restricted Stock and Restricted Stock Units (RSU's) [Member]
Share-based Payment Arrangement, Expense	325,000	$ 267,000	741,000	$ 1,300,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 3,500,000		$ 3,500,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition			2 years 292 days
2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	39,520		469,848
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 13.33
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 5.80		$ 7.22
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	11,928		154,472
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%
2013 Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price			$ 13.33
2013 Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price			$ 16.42