Note 3 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Restricted cash held as a certificate of deposit	$ 324	$ 324
Deposit held as a certificate of deposit	151	151
Total assets	475	475
Warrant liability	3,952	4,089
Embedded derivative liability	1	3
Total liabilities	3,953	4,092
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
Warrant liability
Embedded derivative liability
Total liabilities
Fair Value, Inputs, Level 2 [Member]
Restricted cash held as a certificate of deposit
Deposit held as a certificate of deposit
Total assets
Warrant liability
Embedded derivative liability
Total liabilities
Fair Value, Inputs, Level 3 [Member]
Restricted cash held as a certificate of deposit
Deposit held as a certificate of deposit
Total assets
Warrant liability	3,952	4,089
Embedded derivative liability	1	3
Total liabilities	$ 3,953	$ 4,092