Note 10 - Profit-sharing Plan (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution, Plan Employers Matching Contribution, Annual Vesting Period	6 years
Deferred Profit Sharing [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.4	$ 0.3	$ 0.2