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 other 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 sales of held-to-maturity investments This element represents net sales (purchases) of held-to-maturity investments. Document and Entity Information Amendment Description Amendment Flag Current Fiscal Year End Date Accounts Receivable, Net, Current Accounts receivable, net of allowance for doubtful accounts of $984 at January 28, 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 period Cash and cash equivalents at end of period Increase (Decrease) in Accounts Receivable Accounts receivable Increase (Decrease) in Income Taxes Receivable Income tax receivable Increase (Decrease) in Inventories Inventories Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Accounts Payable Accounts payable Common Stock, Shares Authorized Common stock, Authorized shares Common Stock, Shares, Issued Common stock, Issued 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 - 22,146,714 at January 28, 2012 and 21,949,884 at April 30, 2011 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: 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 on sale of property and equipment Gross Profit Gross margin 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 Stockholders' 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 gain (loss) on long-term investments recorded in other comprehensive income, net of deferred taxes of $59 and $43, respectively Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Unrealized gain (loss) on long-term investments recorded in other comprehensive income, deferred taxes 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 the 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 Provision for Doubtful Accounts Provision for doubtful accounts Payments to Acquire Property, Plant, and Equipment Acquisitions of property and equipment 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 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 Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Supplemental Cash Flow Information [Abstract] Supplemental disclosure: Excess Tax Benefit from Share-based Compensation, Financing Activities Excess tax benefit from stock-based compensation Excess tax benefit from stock-based compensation 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) 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 Scenario, Unspecified [Domain] Statement [Table] Statement, Scenario [Axis] Assets [Abstract] Assets Statement [Line Items] Statement Fair Value Measurements Fair Value Disclosures [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) provided by 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 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 Total stockholders' equity Income Tax Expense (Benefit) Provision for income taxes Preferred Stock, Value, Issued Preferred stock, $0.0001 par value: Authorized shares - 10,000,000 None issued or outstanding Other Comprehensive Income Tax Benefit from Stock Options Exercised Tax benefit from exercise of stock options Liability for Uncertain Tax Positions, Current Liability for uncertain tax positions Liability for Uncertain Tax Positions, Noncurrent Liability for uncertain tax positions Weighted Average Number of Shares Outstanding, Diluted [Abstract] Weighted average shares outstanding: Depreciation, Depletion and Amortization Depreciation and amortization Commitments and Contingencies Commitments and contingencies Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to cash provided by operating activities: Accounts Payable, Current Accounts payable Employee-related Liabilities, Current Wages and related accruals Taxes Payable, Current Income taxes payable Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Organization and Significant Accounting Policies Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest Income before income taxes Prepaid Expense and Other Assets, Current Prepaid expenses and other current assets Net increase in cash and cash equivalents Net Cash Provided by (Used in) Continuing Operations Organization and Significant Accounting Policies Investments Income Taxes Fair Value Measurements Inventories, net Customer-Funded Research & Development Segment Data