Note 7 - Income Tax Expense - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reductions due to lapse of statute of limitations	$ (100)	$ (100)	$ (100)
Excluding Interest and Penalties [Member]
Balance at the beginning of year	477	400
Additions based on tax positions related to the current year	128	56
Additions for tax positions of prior years	173	85
Reductions due to lapse of statute of limitations	(97)	(64)
Balance at the end of year	$ 681	$ 477	$ 400