Note 14 - Concentration (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Revenue from Contract with Customer, Including Assessed Tax	$ 10,210,000	$ 10,080,000	$ 20,538,000	$ 19,697,000
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | One Single Customer [Member]
Concentration Risk, Percentage			31.90%
Revenue from Contract with Customer, Including Assessed Tax			$ 20,538,000