Note 3 - Fair Value Measurements - Fair Value Hierarchy on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Derivative liability - Warrants	$ 899	$ 4,444
Fair Value, Recurring [Member]
Derivative liability - Warrants	899	4,444
Total liabilities	899	4,444
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative liability - Warrants	0	0
Total liabilities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative liability - Warrants	0	0
Total liabilities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative liability - Warrants	899	4,444
Total liabilities	$ 899	$ 4,444