Consolidated Balance Sheets Consolidated Balance Sheets [Abstract] Assets Assets [Abstract] Current assets: Current assets: [Abstract] Cash and cash equivalents Marketable securities Accounts receivable, net of allowance for doubtful accounts of $317 and $430, respectively Inventories Prepaid expenses and other current assets Prepaid income taxes Deferred income taxes Total current assets Property and equipment, net of accumulated depreciation of $19,880 and $18,239, respectively Goodwill Other intangible assets, net of accumulated amortization of $4,064 and $3,385, respectively Deferred income taxes Other assets Total assets Liabilities and Shareholders’ Equity Liabilities and Shareholders’ Equity [Abstract] Current liabilities: Current liabilities: [Abstract] Short-term debt Accounts payable Accrued liabilities: Accrued liabilities: [Abstract] Employee compensation Other accrued liabilities Total current liabilities Other liabilities Total liabilities Shareholders' equity: Shareholders' equity: [Abstract] Common stock, $.01 par value, 40,000,000 shares authorized, 22,039,425 and 23,644,301 shares issued and outstanding, respectively Additional paid-in capital Accumulated deficit Accumulated other comprehensive income Nil coupon perpetual loan notes Total shareholders' equity Total liabilities and shareholders' equity Allowance for doubtful accounts (in Dollars) Accumulated depreciation (in Dollars) Accumulated amortization (in Dollars) Common stock, par value (in Dollars per share) Common stock, shares authorized (in Shares) Common stock, shares issued (in Shares) Common stock outstanding (in Shares) Consolidated Statements of Operations Consolidated Statements of Operations [Abstract] Revenues Costs and expenses: Costs and expenses: [Abstract] Cost of sales Selling, general and administrative Gain on revaluation of ACT liability Gain on revaluation of ACT liability Research and development Operating income Interest expense Interest income Other expense Income before income taxes Income tax expense Net income Net income per common share: Net income per common share: [Abstract] Basic (in Dollars per share) Diluted (in Dollars per share) Weighted-average number of common shares outstanding: Weighted-average number of common shares outstanding: [Abstract] Basic (in Shares) Diluted (in Shares) Consolidated Statements of Comprehensive Income (Unaudited) Consolidated Statements of Comprehensive Income (Unaudited) [Abstract] Net income Other comprehensive income: Other comprehensive income: [Abstract] Foreign currency translation adjustments Unrealized gains/(losses) from marketable securities, net of tax Total other comprehensive income Comprehensive income Consolidated Statements of Cash Flows Consolidated Statements of Cash Flows [Abstract] Operating Activities Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to reconcile net income to net cash provided by operating activities: [Abstract] Depreciation Amortization Gain on equipment disposals Deferred income taxes Stock based compensation Bad debt write-off (recovery) Changes in operating assets and liabilities: Changes in operating assets and liabilities: [Abstract] Accounts receivable Inventories Prepaid expenses, other current assets and other noncurrent assets Accounts payable Accrued liabilities and other noncurrent liabilities Net cash provided by operating activities Investing Activities Investing Activities [Abstract] Proceeds from the sale of equipment Purchases of property, equipment and patents Net cash used in investing activities Financing Activities Financing Activities [Abstract] Proceeds from exercise of stock options Payments to repurchase common stock Excess income tax benefits from exercise of stock options Net cash used in financing activities Effect of exchange rate fluctuations on cash Net decrease in cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Note A - Nature of Business Nature of Operations [Text Block] Note B - Basis of Presentation Basis of Accounting [Text Block] Note C - Revenue Recognition Policy Disclosure of revenue recognition Revenue Recognition [Text Block] Note D - Cost of Sales Cost of Sales, Policy [Policy Text Block] Note E - Selling, General and Administrative Expenses Selling, General and Administrative Expenses, Policy [Policy Text Block] Note F - Available-for-Sale Marketable Securities Marketable Securities, Available-for-sale Securities, Policy [Policy Text Block] Note G - Earnings per Share Data Earnings Per Share [Text Block] Note H - Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Note I - Debt Debt Disclosure [Text Block] Note J - Business Segment and Geographic Disclosures Segment Reporting Disclosure [Text Block] Note K - Contingencies Commitments and Contingencies Disclosure [Text Block] Note L - Income Taxes Income Tax Disclosure [Text Block] Note M - Goodwill and Other Intangibles Goodwill and Intangible Assets Disclosure [Text Block] Note N - Fair Value Fair Value Disclosures [Text Block] Note O - Recently Adopted and Pending Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Note P - Share Repurchase Program Treasury Stock [Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Nonvested Share Activity [Table Text Block] Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block] Schedule of Product Warranty Liability [Table Text Block] Schedule of Treasury Stock by Class [Table Text Block] Basic Earnings Per Share Basic Earnings Per Share [Abstract] Basic weighted-average shares Conversion of unsecured loan notes Unexercised options and RSUs Diluted weighted-average shares Stock-Based Compensation Stock-Based Compensation [Abstract] Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Report Line [Domain] Allocated share based compensation Tax benefit of stock-based compensation expense After-tax effect of stock-based compensation Weighted Average Fair Value Assumptions Weighted Average Fair Value Assumptions [Abstract] Expected dividend yield Risk-free interest rate Expected volatility Expected life of option (years) Stock Option Activity Stock Option Activity [Abstract] Outstanding on January 1, 2012 Outstanding on January 1, 2012 (in Dollars per share) Granted Granted (in Dollars per share) Converted to RSUs Converted to RSUs (in Dollars per share) Exercised Exercised (in Dollars per share) Expired or forfeited Expired or forfeited (in Dollars per share) Outstanding on September 30, 2012 Outstanding on September 30, 2012 (in Dollars per share) Outstanding on September 30, 2012 Exercisable on September 30, 2012 Exercisable on September 30, 2012 (in Dollars per share) Exercisable on September 30, 2012 Non-vested Stock Option Activity Non-vested Stock Option Activity [Abstract] Award Type [Domain] CreationDate [Domain] Non-Vested Stock Options Outstanding Weighted Average Grant Date Fair Value (in Dollars per share) Granted Granted (in Dollars per share) Vested Vested (in Dollars per share) Forfeited Forfeited (in Dollars per share) Restricted Stock Unit Activity Restricted Stock Unit Activity [Abstract] Unvested restricted stock units at December 31, 2011 Unvested restricted stock units at December 31, 2011 (in Dollars per share) Granted Forfeited Unvested restricted stock units at September 30, 2012 Unvested restricted stock units at September 30, 2012 (in Dollars per share) Reporting Segment Net Sales and Gross Margin Reporting Segment Net Sales and Gross Margin [Abstract] Segment [Domain] Revenues from external customers Gross margin Selling, general and administrative Research and development Operating income Gain from revaluation of contingentperformance obligation Operations by Geographic Area Operations by Geographic Area [Abstract] Segment, Geographical [Domain] Revenues: Revenues: [Abstract] Assets Warranty Liability Warranty Liability [Abstract] Aggregate product warranty liability at beginning of period Net aggregate expense related to product warranties Aggregate reductions for payments Aggregate product warranty liability at end of period Share Repurchase Programs Share Repurchase Programs [Abstract] Phase One Program Phase One Program [Abstract] Total Number Of Shares Purchased (in Shares) Average Price Paid Per Share (in Dollars per share) Total Cost Maximum Dollar Value Of Shares That May Yet Be Purchased Under The Program Phase Two Program Phase Two Program [Abstract] Range [Domain] Length of contract Loss on Contract Termination Contract Term Unbilled Receivables, Current Billings in Excess of Cost, Current Marketable Securities, Current Type of Deferred Compensation, All Types [Domain] The amount of shares that may be issued or reserved for awards to participants under a 2004 amendment to the Incentive Plan is 12.5% of outstanding shares calculated on a diluted basis. Stock options granted to employees under the Incentive Plan have a 10-year life and they vest as follows: 50% after the second anniversary of the award date, 25% after the third anniversary, and the final 25% after the fourth anniversary of the award date. Maximum Percent of Shares Allowable In Incentive Plan Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in Shares) Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in Shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares) Share-based Compensation Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Percent of Options Vesting Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share) Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Allocated Share-based Compensation Expense AmountType [Domain] Debt Instrument, Name [Domain] Facility covenants include an annual capital expenditure limit of $10,000 Facility covenants include a minimum tangible net worth of $50,000 Facility covenants include an annual capital expenditure limit of $10,000 and a minimum tangible net worth of $50,000, adjusted upward for 50% of net income generated Facility covenants include an annual capital expenditure limit of $10,000 and a minimum tangible net worth of $50,000, adjusted upward for 50% of net income generated and 100% of all capital issuances. Line of Credit Facility, Expiration Date Line of Credit Facility, Maximum Borrowing Capacity Debt Instrument, Basis Spread on Variable Rate Annual Capital Expenditure Limit Minimum Tangible Net Worth Percentage of Net Income Percentage of Capital Issuances Letters of Credit Outstanding, Amount Line of Credit Facility, Remaining Borrowing Capacity Line of Credit Facility, Commitment Fee Percentage Line of Credit Facility, Amount Outstanding Line of Credit Facility, Interest Rate at Period End Interest Expense, Debt Number of Reportable Segments PaymentFrequency [Domain] Percentage above qualifying gross margin dollars required to pay under the Hurdle agreement Business Acquisition, Contingent Consideration, Potential Cash Payment Business Acquisition, Preacquisition Contingency, Amount Hurdle Agreement Loss Contingency, Estimate of Possible Loss undefined Business Acquisition, Contingent Consideration, at Fair Value Effective income tax rate Recognized Tax Benefit Effective Income Tax Rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate Unrecognized Tax Benefits (in Dollars) Unrecognized Tax Benefits, Period Increase (Decrease) (in Dollars) Recognized Tax Benefit (in Dollars) Effective Income Tax Rate, Continuing Operations Stock Repurchase Program, Authorized Amount Stock Repurchased During Period, Shares (in Shares) Stock Repurchased and Retired During Period, Shares (in Shares) Sales Commissions and Fees Business Segments [Axis] Scenario [Axis] Geographical [Axis] Postretirement Benefits, Type of Deferred Compensation [Axis] Report Date [Axis] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line [Axis] Restricted Stock [Member] Range [Axis] Scenario, Unspecified [Domain] Debt Instrument [Axis] Award Type [Axis] Restricted Stock Units (RSUs) [Member] Maximum [Member] Minimum [Member] Payment Frequency [Axis] Payment Frequency [Axis] Amount Type [Axis] Amount Type [Axis] Fourth Anniversary Of Award Date [Member] Fourth Anniversary of Award Date [Member] Amount Available For Increase Upon Approval Of Lender [Member] Amount Available for Increase Upon Approval of Lender [Member] End Of Period [Member] End of Period [Member] Air Pollution Control Segment [Member] Air Pollution Control Segment [Member] Amended Amount [Member] Amended Amount [Member] Foreign [Member] Foreign [Member] Fuel Chem Technology Segment [Member] Fuel Chem Technology Segment [Member] October 12011 Through December 312011 [Member] October 1 2011 Through December 31 2011 [Member] August 252011 Through September 302011 [Member] August 25 2011 Through September 30 2011 [Member] Stock Option Exchange Plan [Member] Stock Option Exchange Plan [Member] Other Segments [Member] Other Segments [Member] Original Amount [Member] Original Amount [Member] United States [Member] United States [Member] China Facility [Member] China Facility [Member] Deferred Directors Fees [Member] Deferred Directors Fees [Member] Peoples Bank Of China Base Rate [Member] People's Bank of China Base Rate [Member] July 12012through September 302012 [Member] July 1 2012 through September 30 2012 [Member] Beginning Of Period [Member] Beginning of Period [Member] January 12012 Through March 312012 [Member] January 1 2012 Through March 31 2012 [Member] Annual [Member] Annual [Member] APC Technology Segment [Member] APC Technology Segment [Member] Fuel Chem Segment [Member] Fuel Chem Segment [Member] Second Anniversary Of Award Date [Member] Second Anniversary of Award Date [Member] April 12012 Through June 302012 [Member] April 1 2012 Through June 30 2012 [Member] Stock Options And Restricted Stock Units [Member] Stock Options and Restricted Stock Units [Member] Total [Member] Total [Member] Non Vested Stock Options [Member] Non-Vested Stock Options [Member] Third Anniversary Of Award Date [Member] Third Anniversary of Award Date [Member] Document and Entity Information [Abstract] 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RevenueRecognitionTextBlock Schedule of Treasury Stock by Class [Table Text Block] Basis of Accounting [Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Deferred Tax Assets, Net of Valuation Allowance, Noncurrent Business Acquisition, Preacquisition Contingency, Amount Net Cash Provided by (Used in) Investing Activities Document Period End Date Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Product Warranty Accrual Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Earnings Per Share, Basic Amendment Flag Entity Central Index Key Unrecognized Tax Benefits Product Warranty Expense Net Cash Provided by (Used in) Financing Activities Schedule of 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Liabilities Current Fiscal Year End Date Document Fiscal Period Focus Fair Value Disclosures [Text Block] Interest Expense Statement [Table] Statement [Line Items]