LEASES - Operating and finance ROU assets and lease liabilities (Details) - USD ($)	Jul. 31, 2020	Apr. 30, 2020
LEASES
Operating lease right-of-use assets	$ 1,920,000	$ 2,008,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating lease right-of-use assets
Finance Lease, Right-of-Use Asset	$ 12,000	27,000
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property, Plant and Equipment, Net
Total leased assets	$ 1,932,000	2,035,000
Operating Lease, Liability, Current	$ 395,000	395,000
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	is-gaap:OperatingLeaseLiabilityCurrent
Finance Lease, Liability, Current	$ 12,000	27,000
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Finance Lease, Liability, Current
Operating Lease, Liability, Noncurrent	$ 1,817,000	1,879,000
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating Lease, Liability, Noncurrent
Total lease liabilities	$ 2,224,000	$ 2,301,000