Note 3 - Revenue From Contracts With Customers - Changes in Contract Liabilities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Total deferred revenue, beginning of period	$ 800,000	$ 700,000	$ 700,000	$ 700,000
Deferred revenue related to milestones achieved	0	0	100,000	0
Deferred revenue related to milestones achieved, written off due to contract renegotiations	(100,000)	0	(100,000)	0
Total deferred revenue, end of period	$ 700,000	$ 700,000	$ 700,000	$ 700,000