BENEFIT PLANS: (Details Textual) - USD ($)		1 Months Ended				12 Months Ended
	Sep. 04, 2013	Apr. 30, 2018	May 31, 2017	Aug. 31, 2013	Aug. 31, 2012	Apr. 30, 2017	Apr. 30, 2016	Sep. 20, 2016
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation, Total						$ 117,000	$ 68,000
Defined Benefit Plan, Target Plan Asset Allocations						100.00%	100.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets						8.00%	8.00%
Defined Benefit Plan Expected Future Benefit Payments For First Five Years Following Fiscal Year Description						The amount of future annual benefit payments is expected to be between $2,469,000 and $2,798,000 in fiscal years 2018 through 2022, and an aggregate of approximately $11,172,000 is expected to be paid in the fiscal five-year period 2023 through 2027.
Pension Benefit Plan Accelerated Funding						$ 11,688,000
Pension and Other Postretirement and Postemployment Benefit Plans, Liabilities					$ 8,688,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months						1,294,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two						0
Defined Benefit Plan, Expected Future Benefit Payments, Year Three						0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent						1,861,000	$ (268,000)
Equity Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation, Total						66,000	$ 68,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total						$ 54,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period						13,000
Stock Issued During Period, Shares, Restricted Stock Award, Gross						19,500
Two Thousand Six Equity Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number						24,500
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized								500,000
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited						1,000
PBGC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions	$ 3,243,000			$ 3,243,000	$ 3,000,000
Pension and Other Postretirement and Postemployment Benefit Plans, Liabilities	5,019,500			8,688,000
First Lien Mortgages On Real Property Appraised Value				$ 10,039,000
Defined Pension Plan Real Property Of Mortgage						$ 10,034,000
Pension Contributions Towards Accelerated Funding Liability	$ 426,000
PBGC [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions		$ 795,000
PBGC [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions			$ 485,000
Pension and Other Postretirement and Postemployment Benefit Plans, Liabilities			$ 4,534,500
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						29.00%	28.00%
Fixed Income Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						20.00%
Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						50.00%
Other Debt Obligations [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						0.00%
Other Debt Obligations [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						30.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						50.00%
Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						50.00%
Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations						80.00%