12. Employee Benefit Plans (Details)	12 Months Ended
	Apr. 30, 2017 USD ($) $ / shares shares	Apr. 30, 2016 USD ($) $ / shares shares	Apr. 30, 2014 shares	Apr. 30, 1990 shares
12. Employee Benefit Plans (Details) [Line Items]
Stock Issued During Period, Value, Employee Benefit Plan (in Dollars) | $	$ 493,000	$ 498,000
Number of Plans	2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	175,000	72,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,635,125	1,652,625	1,603,125
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	1,280,625
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price (in Dollars per share) | $ / shares	$ 8.35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	35,500	19,500
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	18,563
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized (in Dollars) | $	$ 1,016,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 219 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	159,500	151,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value (in Dollars) | $	$ 694,000	$ 661,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value (in Dollars per share) | $ / shares	$ 3.48	$ 4.06
Employee Benefits and Share-based Compensation (in Dollars) | $	$ 2,519,000	$ 1,450,000
Share-based Compensation (in Dollars) | $	$ 662,000	$ 824,000
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	47,839	46,743
Stock Issued During Period, Value, Employee Benefit Plan (in Dollars) | $	$ 493,000	$ 498,000
Adjustments to Additional Paid in Capital, Share-based Compensation, Employee Stock Purchase Program, Requisite Service Period Recognition (in Dollars) | $	$ 274,000	283,000
Common Stock, Capital Shares Reserved for Future Issuance	738,064
Income Incentive Pool [Member]
12. Employee Benefit Plans (Details) [Line Items]
Accrued Bonuses (in Dollars) | $	$ 272,000	$ 702,000
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) | $ / shares	$ 4.00	$ 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 his 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) | $	$ 2,029,000	$ 959,000
Employee Stock 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	5 years
Employee Benefits and Share-based Compensation (in Dollars) | $	$ 229,000	265,000
Share-based Compensation (in Dollars) | $	424,000	559,000
Deferred Tax Expense from Stock Options Exercised (in Dollars) | $	$ 26,000	$ 141,000
Stock Appreciation Rights (SARs) [Member]
12. Employee Benefit Plans (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 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	2,197,000	2,021,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,635,000	1,653,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	1,281,000	1,314,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price (in Dollars per share) | $ / shares	$ 8.35	$ 8.45
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	35,500	19,500
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	15,273	5,736
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	20,227	13,764