INCOME TAXES - Components of the net deferred income taxes (Details) - USD ($) $ in Thousands	Apr. 30, 2021	Apr. 30, 2020
Deferred income tax assets:
State tax loss carryforwards	$ 4,296	$ 4,622
U.S. federal NOL carryforward	1,384	3,746
Accrued pension costs		1,258
Vacation accrual	14	52
Real estate basis differences	3,976	4,096
Other	303	194
Total deferred income tax assets	9,973	13,968
Deferred income tax liabilities:
Depreciable assets	(749)	(1,341)
Deferred gains on investment assets	(2,300)	(2,277)
Prepaid pension costs	(178)
Other	(31)
Total deferred income tax liabilities	(3,258)	(3,618)
Valuation allowance for realization of certain deferred income tax assets	(3,966)	(4,270)
Net deferred income tax asset	$ 2,749	$ 6,080