Note 4 - Other Accrued Liabilities - Other Accrued Liabilities (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Equipment maintenance and upgrades	$ 502,000	$ 1,281,000
Insurance	227,000	340,000
Professional services	188,000	90,000
Operating costs	384,000	397,000
Other	334,000	311,000
Total other accrued liabilities	$ 1,635,000	$ 2,419,000