Note 11 - Finance Lease Right-of-use - Adoption of ASU 2016-02 (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Increase in depreciation	$ 1,316	$ 415	$ 3,832	$ 1,198
Increase in interest expense	1,112	44	3,296	169
Decrease in net income for the nine months ended January 31, 2020	$ (1,335)	$ (1,340)	(5,626)	$ (3,570)
Accounting Standards Update 2016-02 [Member]
Increase in depreciation			2,118
Increase in interest expense			3,128
Decrease in rent expense			(3,845)
Decrease in net income for the nine months ended January 31, 2020			$ 1,401