Note 4 - Fair Value Measurements - Fair Value of Assets and Liabilities Measured On Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Reported Value Measurement [Member]
Cash and cash equivalents	$ 17,510	$ 24,739
Restricted cash	25	25
Ownership interests	2,407	4,549
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	17,510	24,739
Restricted cash	25	25
Ownership interests	2,407	4,549
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Restricted cash	0	0
Ownership interests	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Restricted cash	0	0
Ownership interests	$ 0	$ 0