Note 3 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Restricted cash held as a certificate of deposit	$ 324	$ 324
Deposit held as a certificate of deposit	151	151
Total assets	475	475
Fair Value, Inputs, Level 1 [Member]
Restricted cash held as a certificate of deposit	324	324
Deposit held as a certificate of deposit	151	151
Total assets	475	475
Fair Value, Inputs, Level 2 [Member]
Restricted cash held as a certificate of deposit	0	0
Deposit held as a certificate of deposit	0	0
Total assets	0	0
Fair Value, Inputs, Level 3 [Member]
Restricted cash held as a certificate of deposit	0	0
Deposit held as a certificate of deposit	0	0
Total assets	$ 0	$ 0