Document and Entity Information Unbilled Contracts Receivable and Retentions, Current This element represents the current portion of Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party, also include retentions amounts withheld by customers until contract completion. Unbilled receivables and retentions Employee Related Liabilities and Other Accruals, Noncurrent Wages and related accruals Aggregate carrying amount, as of the balance sheet date, of employees related liabilities and noncurrent obligations not separately disclosed in the balance sheet. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer).Aggregate carrying amount, as of the balance sheet date, of employees related liabilities and noncurrent obligations not separately disclosed in the balance sheet. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer). Increase (Decrease) in Unbilled Contracts Receivable and Retentions This element represents the net change during the reporting period in the amount of unbilled receivables and retentions. Unbilled receivables and retentions Proceeds from (Payments for) Held-to-maturity Securities Net (purchases) sales of held-to-maturity investments This element represents net sales (purchases) of held-to-maturity investments. Cash Paid During the Year [Abstract] Cash paid during the year for: Other Noncash Investing Items [Abstract] Non-cash investing activities Long-Term Incentive Awards Long-term Incentive Awards Disclosure [Text Block] Long-Term Incentive Awards The entire disclosure of the number, aggregate intrinsic value, performance targets, compensation expenses and weighted-average remaining contractual term for performance-based awards (or share units) at the date of the latest statement of financial position. Amendment Description Amendment Flag Current Fiscal Year End Date Accounts Receivable, Net, Current Accounts receivable, net of allowance for doubtful accounts of $921 at April 30, 2012 and $639 at April 30, 2011 Document Period End Date Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive loss Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Filer Category Entity Public Float Entity Registrant Name Entity Central Index Key Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Period Focus Document Type Additional Paid in Capital, Common Stock Additional paid-in capital Allowance for Doubtful Accounts Receivable, Current Accounts receivable, allowance for doubtful accounts (in dollars) CONSOLIDATED BALANCE SHEETS CONSOLIDATED BALANCE SHEETS Earnings Per Share, Basic Basic (in dollars per share) Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Increase (Decrease) in Accounts Receivable Accounts receivable Increase (Decrease) in Income Taxes Receivable Income tax receivable Increase (Decrease) in Inventories Inventories Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Accounts Payable Accounts payable Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Common Stock, Shares Authorized Common stock, Authorized shares Common Stock, Shares, Issued Common stock, Issued shares Balance (in shares) Balance (in shares) Common Stock, Shares, Outstanding Common stock, outstanding shares Common Stock, Value, Issued Common stock, $0.0001 par value: Authorized shares-100,000,000 Issued and outstanding shares-22,243,903 shares at April 30, 2012 and 21,949,884 at April 30, 2011 Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive Income (Loss) Note [Text Block] Other Comprehensive Income Cost of Goods Sold Product sales Cost of Revenue Total cost of sales Cost of Revenue [Abstract] Cost of sales: Cost of Services Contract services Liabilities, Current Total current liabilities Liabilities, Current [Abstract] Current liabilities: Customer Advances, Current Customer advances Deferred Income Tax Expense (Benefit) Deferred income taxes Deferred Tax Assets, Net, Current Deferred income taxes Earnings Per Share, Diluted Diluted (in dollars per share) Share-based Compensation Stock-based compensation Gain (Loss) on Sale of Property Plant Equipment (Gain) loss on disposition of property and equipment Gross Profit Gross margin Impairment of Long-Lived Assets Held-for-use Impairment of long-lived assets CONSOLIDATED STATEMENTS OF INCOME Income Tax Disclosure [Text Block] Income Taxes Income Taxes Receivable, Current Income tax receivable Increase (Decrease) in Other Operating Assets Other assets Inventory, Net Inventories, net Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Investments Liabilities and Equity Total liabilities and stockholders' equity Liabilities and Equity [Abstract] Liabilities and stockholders' equity Long-term Investments Long-term investments Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations Operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Net Income (Loss) Available to Common Stockholders, Basic Net income Net income Nonoperating Income (Expense) [Abstract] Other income: Operating Income (Loss) Income from operations Revenues Total revenue Revenues [Abstract] Revenue: Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Unrealized gains (losses) on long-term investments recorded in other comprehensive income (loss), net of deferred tax benefit of $56, $16 and $143, respectively Unrealized gain (loss) on investments Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Unrealized gains (losses) on long-term investments recorded in other comprehensive income, deferred tax benefit Preferred Stock, Shares Authorized Preferred stock, Authorized shares Preferred Stock, Shares Issued Preferred stock, issued shares Preferred Stock, Shares Outstanding Preferred stock, outstanding shares Preferred Stock, Par or Stated Value Per Share Preferred stock, par value (in dollars per share) Proceeds from Sale of Available-for-sale Securities Net sales of available-for-sale investments Proceeds from Sale of Property, Plant, and Equipment Proceeds from sale of property and equipment Proceeds from Stock Options Exercised Exercise of stock options Product Warranty Disclosure [Text Block] Warranty Reserves Warranty Reserves Property, Plant and Equipment, Net Property and equipment, net Property and Equipment, net Provision for Doubtful Accounts Provision for doubtful accounts Payments to Acquire Property, Plant, and Equipment Acquisition of property and equipment Related Party Transactions Related Party Transactions Disclosure [Text Block] Research, Development, and Computer Software Disclosure [Text Block] Customer-Funded Research & Development Retained Earnings (Accumulated Deficit) Retained earnings Sales Revenue, Goods, Net Product sales Sales Revenue, Services, Net Contract services Inventory Disclosure [Text Block] Inventories, net Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS Segment Reporting Disclosure [Text Block] Segment Data Selling, General and Administrative Expense Selling, general and administrative Short-term Investments Short-term investments CONSOLIDATED STATEMENTS OF CASH FLOWS CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Supplemental Cash Flow Information [Abstract] Supplemental disclosures of cash flow information Excess Tax Benefit from Share-based Compensation, Financing Activities Excess tax benefit from stock-based compensation Excess tax benefit from stock-based compensation Income taxes Income Taxes Paid Assets, Current Total current assets Assets, Current [Abstract] Current assets: Weighted Average Number of Shares Outstanding, Diluted Diluted (in shares) Weighted Average Number of Shares Outstanding, Basic Basic (in shares) Common Stock Common Stock [Member] Property and Equipment, net Property, Plant and Equipment Disclosure [Text Block] Research and Development Expense Research and development Assets Total assets Investment Income, Interest Interest income Other Liabilities, Current Other current liabilities Deferred Tax Assets, Net, Noncurrent Deferred income taxes Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Scenario, Unspecified [Domain] Statement [Table] Statement, Scenario [Axis] Assets [Abstract] Assets Statement [Line Items] Statement Fair Value Measurements Fair Value Disclosures [Text Block] Quarterly Results of Operations (Unaudited) Quarterly Financial Information [Text Block] Investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity Stockholders' Equity, Period Increase (Decrease) Excess Tax Benefit from Share-based Compensation, Operating Activities Excess tax benefit from stock-based compensation Other Assets, Noncurrent Other assets Earnings Per Share [Abstract] Earnings per share data: Increase (Decrease) in Other Operating Liabilities Other liabilities Deferred Rent Credit, Noncurrent Deferred rent Common Stock, Par or Stated Value Per Share Common stock, par value (in dollars per share) Stockholders' Equity Attributable to Parent