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Note 9 - Share-based Compensation (Details Textual) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2019 $ / shares shares
Number Of Active Stock Incentive Plans	1
Director [Member]
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued (in shares)	12,815	9,772
Share-based Compensation Arrangement by Stock-based Payment Award, Grant Date Fair Value (in dollars per share) | $ / shares	$ 25.37	$ 24.56
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month)	60 months
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	24,000
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 24.15
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)	0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month)	3 years
Performance Shares [Member]
Restricted Stock Units and Performance Share Award Target Level, Percentage	100.00%
Performance Awards Issued Multiplier	136.00%
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number At Target Level Of Performance (in shares)	91,000
Performance Shares [Member] | Minimum [Member]
Performance Awards Issued Multiplier	0.00%
Performance Shares [Member] | Maximum [Member]
Performance Awards Issued Multiplier	200.00%
Restricted Stock Units and Performance Stock Awards [Member]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount | $	$ 3.5
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 9 months 18 days

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