Condensed Consolidated Balance Sheets Condensed Consolidated Balance Sheets [Abstract] Assets Assets [Abstract] Current assets: Current assets: [Abstract] Cash and cash equivalents Fees receivable, net Deferred commissions Prepaid expenses and other current assets Total current assets Property, equipment and leasehold improvements, net Goodwill Intangible assets, net Other assets Total Assets Liabilities and Stockholders’ Equity Liabilities and Stockholders’ Equity [Abstract] Current liabilities: Current liabilities: [Abstract] Accounts payable and accrued liabilities Deferred revenues Current portion of long-term debt Total current liabilities Long-term debt Other liabilities Total Liabilities Stockholders’ Equity Stockholders’ Equity [Abstract] Preferred stock, $.01 par value, 5,000,000 shares authorized; none issued or outstanding Common stock, $.0005 par value, 250,000,000 shares authorized; 156,234,415 shares issued for both periods Additional paid-in capital Accumulated other comprehensive income, net Accumulated earnings Treasury stock, at cost, 62,579,388 and 62,891,251 common shares, respectively Total Stockholders’ Equity Total Liabilities and Stockholders’ Equity Preferred stock par value (in Dollars per share) Preferred stock, shares authorized Preferred stock, shares issued Preferred stock, shares outstanding Common stock par value (in Dollars per share) Common stock, shares authorized Common stock, shares issued Treasury stock, Shares Condensed Consolidated Statements of Operations Condensed Consolidated Statements of Operations [Abstract] Revenues: Revenues: [Abstract] Research Consulting Events Total revenues Costs and expenses: Costs and expenses: [Abstract] Cost of services and product development Selling, general and administrative Depreciation Amortization of intangibles Acquisition and integration charges Total costs and expenses Operating income Interest expense, net Other expense, net Income before income taxes Provision for income taxes Net income Income per common share: Income per common share: [Abstract] Basic (in Dollars per share) Diluted (in Dollars per share) Weighted average shares outstanding: Weighted average shares outstanding: [Abstract] Basic (in Shares) Diluted (in Shares) Condensed Consolidated Statements of Comprehensive Income Condensed Consolidated Statements of Comprehensive Income [Abstract] Net income Other comprehensive income (loss): Other comprehensive income (loss): [Abstract] Foreign currency translation adjustments Unrealized loss on interest rate swap hedge Amortization of pension unrealized actuarial gain Tax effect of comprehensive income items Other comprehensive income (loss), net of tax effect Comprehensive income Condensed Consolidated Statements of Cash Flows Condensed 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 and amortization of intangibles Stock-based compensation expense Excess tax benefits from stock-based compensation Deferred taxes Amortization of debt issue costs Changes in assets and liabilities, net of acquisition: Changes in assets and liabilities, net of acquisition: [Abstract] Fees receivable, net Deferred commissions Prepaid expenses and other current assets Other assets Deferred revenues Accounts payable, accrued, and other liabilities Cash provided by operating activities Investing activities: Investing activities: [Abstract] Additions to property, equipment and leasehold improvements Acquisition (net of cash acquired) Cash used in investing activities Financing activities: Financing activities: [Abstract] Proceeds from stock issued under stock plans Proceeds from debt issuance Payments on debt Purchases of treasury stock Excess tax benefits from stock-based compensation Cash used by financing activities Net increase in cash and cash equivalents Effects of exchange rates on cash and cash equivalents Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Business and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Acquisition Business Combination Disclosure [Text Block] Earnings per Share Earnings Per Share [Text Block] Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Segment Information Segment Reporting Disclosure [Text Block] Goodwill and Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Debt Debt Disclosure [Text Block] Equity Stockholders' Equity Note Disclosure [Text Block] Income Taxes Income Tax Disclosure [Text Block] Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure [Text Block] Fair Value Disclosures Fair Value Disclosures [Text Block] Employee Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Significant Accounting Policies (Abstract) Significant Accounting Policies Consolidation, Policy [Policy Text Block] Use of Estimates, Policy [Policy Text Block] Schedule of Purchase Price Allocation [Table Text Block] Schedule of Earnings Per Share Reconciliation [Table Text Block] Award Type [Domain] Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Schedule of Share-based Compensation, Stock Appreciation Rights Award Activity [Table Text Block] Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Intangible Assets and Goodwill [Table Text Block] Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Schedule of Debt [Table Text Block] Schedule of Treasury Stock by Class [Table Text Block] Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Aggregate Preliminary Purchase Price Allocation to Assets Acquired and Liabilities Assumed in Acquisition Aggregate Preliminary Purchase Price Allocation to Assets Acquired and Liabilities Assumed in Acquisition [Abstract] Business Acquisition, Acquiree [Domain] Assets: Assets: [Abstract] Cash Fees receivable Prepaid expenses and other current assets Business acquisition, purchase price allocation, intangible assets and goodwill. Goodwill and amortizable intangible assets (1) Total assets Liabilities: Liabilities: [Abstract] Business Acquisition, Purchase Price Allocation, Accounts Payable and Accrued Liabilities. Accounts payable and accrued liabilities Business Acquisition, Purchase Price Allocation, Deferred Revenue. Deferred revenues (2) Total liabilities Goodwill Amortizable intangible assets Calculations Of Basic And Diluted Earnings Per Share Calculations Of Basic And Diluted Earnings Per Share [Abstract] Numerator: Numerator: [Abstract] Net income used for calculating basic and diluted earnings per share (in Dollars) Denominator: Denominator: [Abstract] Weighted average number of common shares used in the calculation of basic earnings per share Common stock equivalents associated with stock-based compensation plans (1) Shares used in the calculation of diluted earnings per share Basic earnings per share (in Dollars per share) Diluted earnings per share (in Dollars per share) Common stock equivalents that were not included in the computation of diluted earnings per share because the effect would have been anti-dilutive Stock-Based Compensation Expense By Award Type Stock-Based Compensation Expense By Award Type [Abstract] Stock-based compensation expense Total expense (1) Stock-Based Compensation Expense Recognized In Consolidated Statements Of Operations Stock-Based Compensation Expense Recognized In Consolidated Statements Of Operations [Abstract] Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Report Line [Domain] Stock-based compensation expense Stock-based compensation expense Summary Of Changes In SARs Outstanding Summary Of Changes In SARs Outstanding [Abstract] Plan Name [Domain] Outstanding (in Shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Exercise Price. Per Share Weighted- Average Exercise Price Per Share Weighted- Average Grant Date Fair Value