Statement of Financial Position [Abstract] Cash and cash equivalents Marketable securities Accounts receivable, net of allowance for doubtful accounts of $111 at April 30, 2022 and April 30, 2021 Contract assets Inventories, net Prepaid income taxes Prepaid expenses and other Total current assets Property, plant and equipment, at cost, net of accumulated depreciation and amortization Goodwill Cash surrender value of life insurance Other assets Total assets Identifiable Assets Accounts payable – trade Accrued liabilities Total current liabilities Deferred compensation Total liabilities Commitments and contingencies (Note 16) Preferred stock - $1.00 par value; authorized 600 shares, no shares issued Preferred stock, par value (in Dollars per share) Preferred stock, shares authorized Preferred stock, shares issued Common stock - $1.00 par value; authorized 20,000 shares, 9,298 shares issued and 9,297 shares outstanding at April 30, 2022; 9,226 shares issued and 9,225 shares outstanding at April 30, 2021 Common stock, shares authorized Additional paid-in capital Accumulated deficit Common stock reacquired and held in treasury - at cost (1 share at April 30, 2022 and April 30, 2021) Accumulated other comprehensive income (loss) Total stockholders’ equity Balance Balance Total liabilities and stockholders’ equity Income Statement [Abstract] Revenues Revenues Revenue Cost of revenues Gross margin Selling and administrative expenses Research and development expenses Operating loss Operating profit (loss) Investment income Interest expense Other income (expense), net (Loss) income before provision (benefit) from income taxes Provision (benefit) from income taxes Total (benefit) provision Net (loss) income Net (loss) income Net income (loss) Basic and diluted (loss) earnings per share (in Dollars per share) Basic (in Shares) Basic EPS Shares outstanding (weighted average) Change in market value of marketable securities before reclassification, net of tax Items of other comprehensive income (loss) before reclassification, net of taxes Total unrealized loss on marketable securities, net of tax Comprehensive (loss) income Statement of Cash Flows [Abstract] Depreciation and amortization Provision for losses on accounts receivable, inventories, other assets and warranty reserve Gain on marketable securities Loss on sale of fixed and other assets, net Employee benefit plans expense Employee Benefits and Share-Based Compensation (in Dollars) Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense (in Dollars) Accounts receivable Contract assets Inventories Prepaid expenses and other Other assets Accounts payable - trade Accrued liabilities Loss provision accrual Income taxes refundable Other liabilities Net cash provided by operating activities Purchase of marketable securities Proceeds from sale or redemption of marketable securities Capital expenditures Net cash used in investing activities Net cash used in financing activities Net increase in cash and cash equivalents Cash and cash equivalents at beginning of year Cash and equivalents at end of year Interest Income taxes Statement of Stockholders' Equity [Abstract] Balance (in Shares) Balance (in Shares) Common stock shares outstanding Contribution of stock to 401(k) plan Stock Issued During Period, Value, Employee Benefit Plan (in Dollars) Contribution of stock to 401(k) plan (in Shares) Stock Issued During Period, Shares, Employee Benefit Plan Stock-based compensation expense Stock-based compensation expense (in Shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Exercise of stock options and stock appreciation rights - net of Exercise of stock options and stock appreciation rights - net of (in Shares) Options, Shares Exercised Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Equity Components [Axis] Accounting Policies [Abstract] Disaggregation of Revenue [Abstract] Segments [Axis] Accounting Standards Update [Axis] Revenue from External Customers by Products and Services [Abstract] Product and Service [Axis] Earnings Per Share [Abstract] Schedule of Earnings Per Share, Basic and Diluted [Abstract] Diluted EPS Shares outstanding Diluted (in Shares) Contractors [Abstract] Costs and Estimated Earnings in Excess of Billings, Net [Abstract] Contract Assets Contract Liabilities Net (liability) asset Inventory Disclosure [Abstract] Schedule of Inventory, Current [Abstract] Raw Materials and Component Parts Work in Progress Finished Goods Property, Plant and Equipment [Abstract] Schedule of Property, Plant and Equipment [Abstract] Buildings and building improvements Machinery, equipment and furniture Less accumulated depreciation Disclosure Text Block [Abstract] Lease, Cost [Abstract] Total lease liabilities Present value of future lease payments Lessee, Operating Lease, Liability, Maturity [Abstract] Total lease payments Investments, Debt and Equity Securities [Abstract] Schedule of Available-for-Sale Securities Reconciliation [Abstract] Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Schedule of Unrealized Gain (Loss) on Investments [Abstract] Financial Instrument [Axis] Fair Value, Less than 12 months Unrealized Losses, Less than 12 months Fair Value, Morethan 12 months Unrealized Losses, More than 12 months Fair Value Unrealized Losses Schedule of Realized Gain (Loss) on Investments [Abstract] Schedule of Fair Value, by Balance Sheet Grouping [Abstract] Current Due after one year through five years Due after five years Debt Disclosure [Abstract] Payables and Accruals [Abstract] Schedule of Accrued Liabilities [Abstract] Vacation and other compensation Incentive compensation Payroll taxes Warranty reserve Commissions Other Investment Holdings [Abstract] Disclosure Text Block Supplement [Abstract] Schedule of Share-based Compensation, Stock Options, Activity [Abstract] Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Abstract] Award Type [Axis] Income Tax Disclosure [Abstract] Schedule of Components of Income Tax Expense (Benefit) [Abstract] Federal State Current (benefit) provision Federal State Deferred tax (benefit) provision Schedule of Effective Income Tax Rate Reconciliation [Abstract] Statutory rate State and local tax Valuation allowance on deferred tax assets Nondeductible expenses Uncertain tax positions Nontaxable life insurance cash value increase Tax credits Change in tax rate Other items Schedule of Deferred Tax Assets and Liabilities [Abstract] Employee benefits Inventory Accounts receivable Tax credits Other assets Capital Loss carry-forward Net operating loss carryforwards Total deferred tax asset Property, plant and equipment Other liabilities Deferred state income tax Net deferred tax asset Valuation allowance Schedule of Unrecognized Tax Benefits Roll Forward [Abstract] Balance at the beginning of the fiscal year Balance at the end of the fiscal year