Note 7 - Income Tax Expense (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total	$ 0.2	$ 0.2	$ 0.1
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0.1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	0.2	0.2
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 0.3
Domestic Tax Authority [Member]
Open Tax Year	2017
State and Local Jurisdiction [Member]
Open Tax Year	2014 2015 2016 2017 2018 2019 2020
Other Noncurrent Liabilities [Member]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 1.2	$ 0.9