BENEFIT PLANS - Changes in the pension plan's benefit obligation and assets (Details) - USD ($)	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
BENEFIT PLANS
Benefit obligation at beginning of year	$ 23,274,000	$ 30,304,000
Interest cost	504,000	716,000
Actuarial loss (gain)	(537,000)	1,550,000
Benefits paid	(1,663,000)	(2,016,000)
Settlement paid		(7,280,000)
Benefit obligation at end of year	21,578,000	23,274,000
Change in plan assets:
Fair value of plan assets at beginning of year	18,260,000	23,903,000
Actual return on plan assets	2,808,000	393,000
Company contributions	1,847,000	3,600,000
Benefits paid	(1,663,000)	(2,016,000)
Settlement paid		(7,280,000)
Plan expenses	(150,000)	(340,000)
Fair value of plan assets at end of year	21,102,000	18,260,000
Underfunded status	$ (476,000)	$ (5,014,000)