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12. Employee Benefit Plans (Details) - USD ($)	12 Months Ended
12. Employee Benefit Plans (Details) - USD ($)	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 1990
12. Employee Benefit Plans (Details) [Line Items]
Stock Issued During Period, Value, Employee Benefit Plan (in Dollars)	$ 412,000	$ 433,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	162,500	25,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,499,750	1,488,000		1,635,125
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	1,216,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 9.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	145,750	3,500
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	81,966
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount (in Dollars)	$ 635,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years 146 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	104,250	151,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value (in Dollars)	$ 403,000	$ 628,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value (in Dollars per share)	$ 3.01	$ 2.71
Employee Benefits and Share-based Compensation (in Dollars)	$ 1,672,000	$ 1,294,000
Share-based Payment Arrangement, Noncash Expense (in Dollars)	$ 500,000	$ 470,000
Shares Issued, Shares, Share-based Payment Arrangement, before Forfeiture		2,850	1,100
Share-based Payment Arrangement, Option [Member]
12. Employee Benefit Plans (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Employee Benefits and Share-based Compensation (in Dollars)	$ 190,000	$ 168,000
Share-based Payment Arrangement, Noncash Expense (in Dollars)	$ 298,000	$ 275,000
Stock Appreciation Rights (SARs) [Member]
12. Employee Benefit Plans (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	5 years
Stock Appreciation Rights (SARs) [Member] \| Employees and Directors [Member]
12. Employee Benefit Plans (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	2,384,000	2,222,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,500,000	1,488,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	1,216,000	1,260,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 9.12	$ 8.55
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	145,750	3,500
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture	71,111	861
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	74,639	2,639
United States Post-Retirement Benefit Plan of US Entity, Defined Benefit [Member]
12. Employee Benefit Plans (Details) [Line Items]
Stock Issued During Period, Shares, Employee Benefit Plan	41,211	46,628
Stock Issued During Period, Value, Employee Benefit Plan (in Dollars)	$ 412,000	$ 433,000
APIC, Share-based Payment Arrangement, ESPP, Increase for Cost Recognition (in Dollars)	$ 223,000	219,000
Common Stock, Capital Shares Reserved for Future Issuance	623,672
Income Incentive Pool [Member]
12. Employee Benefit Plans (Details) [Line Items]
Accrued Bonuses (in Dollars)	$ 195,000	$ 60,000
Restricted Stock Plan [Member]
12. Employee Benefit Plans (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	7,500	7,500			375,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercise Price (in Dollars per share)	$ 4.00
Deferred Compensation Agreement [Member]
12. Employee Benefit Plans (Details) [Line Items]
Deferred Compensation Arrangement with Individual, Description		Under these agreements, each key employee receives specified retirement payments for the remainder of the employee’s life with a minimum payment of ten years’ benefits to either the employee or their beneficiaries. The agreements also provide for lump sum payments upon termination of employment without cause and reduced benefits upon early retirement.
Deferred Compensation Arrangement with Individual, Compensation Expense (in Dollars)	$ 1,300,000	$ 909,000