| Note 7 - Convertible Note Payable | 9 Months Ended | 
|---|---|
| Sep. 30, 2020 | |
| Notes to Financial Statements | |
| Long-term Debt [Text Block] | 7. Convertible Note Payable 
 On January 24, 2019, the Company repaid Interstate Battery the outstanding principal and interest on the convertible debt in the amount of $6.7 million. In connection with the payoff, the Company amortized the remaining discount on the note of $2.6 million and remaining deferred financing expenses of $20,000 to interest expense. 
 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- Definition The entire disclosure for long-term debt. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 |