Note 6 - Note Payable - Summary of Note Payable (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	[1]
Less: Unamortized debt discount	$ (6,000)
Note payable, noncurrent portion	4,964,000	$ 4,518,000
The 2017 Loan Agreement [Member]
2021 (remaining 3 months)	0
2022	0
2023	5,992,000
Total Payments	5,992,000
Less: Amount representing interest	(1,022,000)
Present value of obligations	4,970,000
Less: Unamortized debt discount	(6,000)
Note payable, noncurrent portion	$ 4,964,000

[1] The condensed consolidated balance sheet as of December 31, 2020 has been derived from the audited consolidated financial statements as of that date.