Note 3 - Contracts With Customers 2 (Details Textual) - Long-term Contract with Customer [Member] - USD ($)	Sep. 30, 2021	Mar. 31, 2021
Revenue, Remaining Performance Obligation, Amount	$ 3,200,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)		3 months
Revenue, Remaining Performance Obligation, Amount	153,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)		1 year
Revenue, Remaining Performance Obligation, Amount	1,400,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)		1 year
Revenue, Remaining Performance Obligation, Amount	1,100,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)		1 year
Revenue, Remaining Performance Obligation, Amount	$ 587,000