ASSETS Assets [Abstract] Total assets (including $1,476,304 in 2011 and $1,410,626 in 2010 from VIEs) Assets Total assets Brokers, dealers and clearing organizations (including $177,889 in 2011 and $195,485 in 2010 from VIEs) Securities purchased under agreements to resell Securities Purchased under Agreements to Resell Securities borrowed Securities Borrowed Investments in managed funds The fair value as of the balance sheet date of the firm's investments in funds managed by us and investments in third-party managed funds in which we are entitled to a portion of the management and/or performance fees. Investments in managed funds Financial Instruments, Owned, Derivatives and Other Contractual Agreements, at Fair Value Derivatives Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value Mortgage- and asset-backed securities Financial Instruments, Owned, Corporate Equities, at Fair Value Corporate equity securities Cash and Securities Segregated under Federal and Other Regulations Liabilities and Stockholders' Equity [Abstract] LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Stockholders' Equity Total liabilities and stockholders' equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] STOCKHOLDERS' EQUITY Accumulated other comprehensive loss: Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Financial instruments sold, not yet purchased, at fair value: Financial Instruments Sold, Not yet Purchased, at Fair Value [Abstract] Liabilities Total liabilities Mandatorily Redeemable Preferred Interest Of Consolidated Subsidiaries Mandatorily redeemable preferred interest of consolidated subsidiaries (including $327,790 in 2011 and $315,885 in 2010 from VIEs) Mandatorily redeemable preferred interest of consolidated subsidiaries Represents nonconsolidated mandatorily redeemable interests held in Jefferies High Yield Holdings, LLC ("JHYH"), which are entitled to a pro rata share of the profits and losses of JHYH and are scheduled to terminate in 2013, with an option to extend up to three additional one-year periods. Financial instruments issued by a subsidiary that are classified as equity in the subsidiary's financial statements are treated as noncontrolling interests in the consolidated financial statements. Less: Treasury stock, at cost, 9,994,438 shares in 2011 and 28,607,510 shares in 2010 Mandatorily redeemable convertible preferred stock Mandatorily redeemable convertible preferred stock Represents the purchase price of Series A convertible preferred stock. Customers Payables to Customers Securities sold under agreements to repurchase Securities Sold under Agreements to Repurchase Total financial instruments sold, not yet purchased, at fair value Total financial instruments sold, not yet purchased, at fair value (including $435,161 in 2011 and $596,044 in 2010 from VIEs) Mortgage- and asset-backed securities Financial Instruments Sold, Not yet Purchased, Mortgages, Mortgage-backed and Asset-backed Securities Financial Instruments Sold, Not yet Purchased, Corporate Debt Corporate debt securities Corporate equity securities (including $0 in 2011 and $2,708 in 2010 from VIEs) Financial Instruments Sold, Not yet Purchased, Corporate Equities Corporate equity securities Revenues: Revenues [Abstract] Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net earnings Net earnings Consolidated Statements of Financial Condition [Abstract] Statement [Table] Statement [Line Items] Consolidated Statements of Earnings [Abstract] Business development Business Development Occupancy and equipment rental Occupancy, Net Net revenues, less mandatorily redeemable preferred interest The portion of net earnings (loss) after Mandatorily redeemable preferred interest from Net revenues. Net revenues, less mandatorily redeemable preferred interest Interest on mandatorily redeemable preferred interest of consolidated subsidiaries Interest on mandatorily redeemable preferred interest of consolidated subsidiaries Represents the allocation of earnings and losses from our consolidated high yield business to third party noncontrolling interest holders invested in that business through mandatorily redeemable preferred securities. Revenues, Net of Interest Expense Net revenues Net revenues Interest Expense Interest expense Interest Interest Income, Operating Investment banking Investment Banking Revenue Commissions Brokerage Commissions Revenue Basic Earnings Per Share, Basic, Total Earnings Per Share, Basic Diluted Earnings Per Share, Diluted, Total Earnings Per Share, Diluted Basic Weighted Average Number of Shares Outstanding, Basic, Total Weighted Average Number of Shares Outstanding, Basic Diluted Weighted Average Number of Shares Outstanding, Diluted, Total Weighted Average Number of Shares Outstanding, Diluted Earnings per common share: Net increase (decrease) in cash and cash equivalents Payment To Mandatorily Redeemable Preferred Interest Of Consolidated Subsidiaries Mandatorily redeemable preferred interest of consolidated subsidiaries Change in nonconsolidated mandatorily redeemable interests held in Jefferies High Yield Holdings, LLC ("JHYH"), which are entitled to a pro rata share of the profits and losses of JHYH and are scheduled to terminate in 2013. Excess tax benefits from the issuance of share-based awards Excess Tax Benefit from Share-based Compensation, Financing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities (Decrease) increase in securities sold under agreements to repurchase Increase in financial instruments sold, not yet purchased Increase (Decrease) in Financial Instruments Sold, Not yet Purchased Brokers, dealers and clearing organizations Increase (Decrease) in Payables to Broker-Dealers (Increase) decrease in securities purchased under agreements to resell (Increase) decrease in investments in managed funds Decrease (increase) in investments in managed funds The net change during the reporting period of the investments in funds managed by the firm and investments in third-party managed funds in which we are entitled to a portion of the management and/or performance fees. Increase in securities borrowed Increase (Decrease) in Securities Borrowed Interest on mandatorily redeemable preferred interests of consolidated subsidiaries Interest on mandatorily redeemable preferred interests of consolidated subsidiaries The net change during the reporting period of nonconsolidated mandatorily redeemable interests held in Jefferies High Yield Holdings, LLC ("JHYH"), which are entitled to a pro rata share of the profits and losses of JHYH. Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Adjustments to reconcile net earnings to net cash used in operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Increase (Decrease) in Receivables [Abstract] Increase in receivables: Stock Issued During Period, Value, New Issues Issued Issued Benefit plan share activity Inclusive of grants related to the incentive plan, deferred compensation plan, and directors plan. Benefit plan share activity Share-based expense, net of forfeitures and clawbacks Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Value Proceeds from exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Comprehensive income Comprehensive Income, Net of Tax, Attributable to Parent Common Stock, Par or Stated Value Per Share Earnings Per Share [Text Block] Derivative Financial Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Securitization Activities and Variable Interest Entities [Abstract] Securitization Activities and Variable Interest Entities. Long-Term Debt Long-term Debt [Text Block] Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Compensation Plans Compensation Related Costs, General [Text Block] Income Taxes Income Tax Disclosure [Text Block] Segment Reporting Segment Reporting Disclosure [Text Block] Related Party Transactions Related Party Transactions Disclosure [Text Block] Financial Instruments Owned Loans And Other Receivables Loans and other receivables (including $480,918 in 2011 and $362,465 in 2010 from VIEs) Loans and other receivables The fair value as of the balance sheet date of firm holdings in corporate loans, participation certificates in GNMA project and construction loans, and escrow and trade claim receivables. Financial Instrument Owned Government Federal Agency And Other Sovereign Obligations Government, federal agency and other sovereign obligations The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term treasury bills, medium-term treasury notes, long term treasury bonds, as well as debt issued by agencies and firm holdings in fixed income obligations issued by foreign governments (includes both pledged to counterparties as collateral for financing transactions and unpledged holdings. Financial Instrument Sold Not Yet Purchased Government Federal Agency And Other Sovereign Obligations Government, federal agency and other sovereign obligations Fair value as of the balance sheet date of obligations incurred arising from US treasury and other US government, agency obligations, and foreign government debt sold short. Asset management fees and investment income (loss) from managed funds Asset management fees and investment income from managed funds Revenues earned from management, administrative and performance fees from funds managed by the firm, third-party managed funds, and investment income (loss) from investments in these funds. Total non-interest expenses Noninterest Expense Supplemental disclosures of cash flow information: Supplemental Cash Flow Information [Abstract] Interest Interest Paid Returns Forfeitures Treasury Stock Returns / forfeitures Employee shares returned to Jefferies as a result of restricted stock forfeiture provisions. Securitization Activities and Variable Interest Entities [Text Block] Securitization Activities and Variable Interest Entities Provides disclosures pertaining to transfers of financial assets accounted for as sales and secured borrowings, how the transfer of financial assets affects an entity's financial position, financial performance, and cash flows and continuing involvement in these securitized assets. Also includes disclosure of variable interest entities (VIE), including, but not limited to the nature, purpose, size, and activities of the VIE, the carrying amount and classification of consolidated assets that are collateral for the VIE's obligations, and interests in VIEs that are not consolidated. Short-Term Borrowings Short-term Debt [Text Block] Non-interest expenses: Noninterest Expense [Abstract] Mandatorily Redeemable Convertible Preferred Stock [Abstract] Mandatorily Redeemable Convertible Preferred Stock [Abstract] Mandatorily Redeemable Convertible Preferred Stock. Mandatorily Redeemable Convertible Preferred Stock [Text Block] Mandatorily Redeemable Convertible Preferred Stock Disclosure of the purchase or issuance of our Series A convertible preferred stock. Consolidated Statement of Changes in Stockholders' Equity [Abstract] Consolidated Statements of Comprehensive Income [Abstract] Entity Registrant Name Entity Central Index Key Document Type Document Period End Date Amendment Flag Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Filer Category Entity Public Float Entity Common Stock, Shares Outstanding Common stock, shares authorized Common stock, shares authorized Statement, Equity Components [Axis] Equity Component [Domain] Parent [Member] Consolidated Statements of Cash Flows [Abstract] Document Fiscal Year Focus Document Fiscal Period Focus Net Proceeds Payments From Equity And Debt Financing [Abstract] Net proceeds from (payments on): Net Proceeds Payments From Equity And Debt Financing. Securities received as collateral Securities Received as Collateral Document and Entity Information [Abstract] Document and Entity Information Abstract. Payables [Abstract] Payables: Payables. Weighted Average Common Shares [Abstract] Weighted average common shares: Weighted average common shares. Other Comprehensive Income (Loss), Net of Tax [Abstract] Increase (Decrease) in Operating Liabilities [Abstract] Increase in payables: Decrease Increase In Cash And Securities Segregated And On Deposit For Regulatory Purposes Or Deposited With Clearing And Depository Organizations Decrease (increase) in cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations The net change during the reporting period of the amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances and cash and securities segregated in compliance with regulations. Increase Decrease In Customers Receivable Customers The net change during the reporting period of the amounts due from customers for fees and charges arising from transactions related to the entity's brokerage activities and operations. Increase Decrease In Customers Payable Customers The net change in amounts payable to customers at the balance sheet date. Dividend equivalents on share-based plans Dividend equivalents on share-based plans Value of additional restricted stock units awarded to holders as a result of dividend declarations. Noncontrolling Interest, Increase from Stock Issuance or Sale of Parent Equity Interest Contributions Cash paid received during the period [Abstract] Cash paid during the year for: Cash paid (received) during the period for: Noncontrolling Interest and Mandatorily Redeemable Preferred Interests of Consolidated Subsidiaries [Abstract] Noncontrolling Interest and Mandatorily Redeemable Preferred Interests of Consolidated Subsidiaries. Noncontrolling Interest and Mandatorily Redeemable Preferred Interests of Consolidated Subsidiaries [Text Block] Noncontrolling Interest and Mandatorily Redeemable Preferred Interests of Consolidated Subsidiaries Disclosure of the equity interests in consolidated subsidiaries that are not attributable, either directly or indirectly, to the firm and the Mandatorily redeemable financial interest issued by Jefferies High Yield Holdings, LLC ("JHYH"). Obligation to Return Securities Received as Collateral Accumulated other comprehensive (loss) income Accumulated other comprehensive (loss) income Increase (Decrease) in Brokerage Receivables Brokers, dealers and clearing organizations Brokers, dealers and clearing organizations Common Stock, Value, Outstanding Increase Decrease In Other Investments Increase in other investments The net change during the reporting period of in investments in and advances to affiliates, subsidiaries, associates, and joint ventures Fees Interest And Other Fees, interest and other (including $6,925 in 2011 and $127 in 2010 from VIEs) Fees, interest and other Represents accounts receivable from clients, counterparties and others, interest income receivable, dividend income receivable, fees receivable, and other receivables from suppliers, insurance companies and amounts due from third parties. Distribution To Noncontrolling Interest Noncontrolling interest The cash outflow from any dividend or other distribution in cash with respect to any shares of, or other ownership interest, including distribution of earnings or stock dividend. Loans Financial Instruments Sold Not Yet Purchased Loans (including $162,285 in 2011 and $150,100 in 2010 from VIEs) Loans The fair value as of the balance sheet date of firm holdings in corporate loans, participation certificates in GNMA project and construction loans held in a short position. Derivatives Financial Instruments Sold Not Yet Purchased Derivatives (including $0 in 2011 and $136 in 2010 from VIEs) Derivatives Fair value as of the balance sheet date of obligations incurred arising from derivative and other contracts on a net basis. Professional Fees Professional services Fees related to assigned management agreements Management Fees Revenue Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Asset Cash received from contingent consideration Deconsolidation Of Asset Management Entity Deconsolidation of asset management entity Decrease in noncontrolling interest from the deconsolidation of an entity related to our asset management activities due to changes in nature and level of our investment in the entity. Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Subsidiary Company [Abstract] Subsidiary Company. Subsidiary Company [Text Block] Jefferies Finance LLC Subsidiary Company. Contingent Consideration Acquisitions and contingent consideration Current share issuances relating to earn-out provisions of acquisitions. Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entity, Classification [Domain] Restatement Adjustment [Member] Restatement Adjustment Adjustments for New Accounting Pronouncement [Member] Adjustments for New Accounting Pronouncement Financial Instruments, Owned, at Fair Value, by Type, Alternative [Abstract] Financial Instruments, Owned, Corporate Debt, at Fair Value Corporate debt securities Statement, Scenario [Axis] Scenario, Unspecified [Domain] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Commitments Contingencies and Guarantees [Text Block] Commitments, Contingencies and Guarantees Proceeds from Issuance of Senior Long-term Debt Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net [Abstract] Acquisitions: Business Acquisition, Purchase Price Allocation, Assets Acquired Fair value of assets acquired, including goodwill Business Acquisition, Purchase Price Allocation, Liabilities Assumed Liabilities assumed Business Acquisition, Cost of Acquired Entity, Cash Paid Cash paid for acquisition Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Organization and basis of Presentation Collateralized Transactions [Abstract] Collateralized Financing. Acquisitions [Abstract] Business Combination Disclosure [Text Block] Acquisitions Short-Term Borrowings/Long-Term Debt [Abstract] Compensation Plans [Abstract] Net Capital Under Securities And Exchange Commission Regulation [Text Block] Net Capital Requirements Net capital under securities and exchange commission regulation. Organization and Basis of Presentation [Abstract] Summary of Significant Accounting Policies [Abstract] Financial Instruments [Abstract] Fair Value Disclosures [Text Block] Financial Instruments Derivative Financial Instruments [Abstract] Benefit Plans [Abstract] Income Taxes [Abstract] Net Capital Requirements [Abstract] Segment Reporting [Abstract] Related Party Transactions [Abstract] Earnings per Share [Abstract] Earnings per Share Proceeds from Short-term Debt Gross proceeds from short-term borrowings Repayments of Short-term Debt Gross payments on short-term borrowings Financial Instruments, Owned, Principal Investments, at Fair Value Investments, at fair value Financial Instruments, Owned, at Fair Value Total financial instruments owned, at fair value Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Cash and cash equivalents at beginning of period Cash and cash equivalents Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Other investments Receivables from Brokers-Dealers and Clearing Organizations Brokers, dealers and clearing organizations Receivables from Customers Customers Property, Plant and Equipment, Net Premises and equipment Goodwill Goodwill Financial Instruments Sold, Not yet Purchased, at Fair Value Securities Loaned Securities loaned Obligation to return securities received as collateral Payables to Broker-Dealers and Clearing Organizations Brokers, dealers and clearing organizations Accounts Payable and Accrued Liabilities Accrued expenses and other liabilities Long-term Debt Long-term debt Additional Paid in Capital, Common Stock Additional paid-in capital Retained Earnings (Accumulated Deficit) Retained earnings Treasury Stock, Value Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Currency translation adjustments Accumulated Other Comprehensive Income (Loss), Net of Tax Total accumulated other comprehensive loss Pledged Financial Instruments, Not Separately Reported, Securities Securities pledged to creditors Common Stock, Shares, Issued Common stock, shares issued Treasury Stock Shares Treasury stock, at cost Principal Transactions Revenue Principal transactions Labor and Related Expense Compensation and benefits Floor Brokerage, Exchange and Clearance Fees Floor brokerage and clearing fees Communications and Information Technology Technology and communications Treasury Stock, Value, Acquired, Cost Method Purchases Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Distributions Common stock, par value Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Share-based Compensation Accruals related to various benefit plans and stock issuances, net of estimated forfeitures Increase (Decrease) in Other Receivables Fees, interest and other Increase (Decrease) in Financial Instruments Used in Operating Activities Increase in financial instruments owned Increase (Decrease) in Other Operating Assets Increase in other assets Issuance of senior notes, net of issuance costs Payments for Repurchase of Common Stock Repurchase of common stock Payments of Dividends, Common Stock Dividends Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest Earnings before income taxes Revenues Total revenues Stockholders' Equity Attributable to Parent Balance, end of period Balance, beginning of period Total common stockholders' equity Total common stockholders' equity Proceeds from Stock Options Exercised Exercise of stock options, not including tax benefits Other Assets Other assets Income Tax Expense (Benefit) Income tax expense Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability Cash paid for contingent consideration Accumulated Other Comprehensive Income (Loss), Defined Benefit Pension and Other Postretirement Plans, Net of Tax Additional minimum pension liability Other Income Other Other Comprehensive Income, Foreign Currency Transaction and Translation Adjustment, Net of Tax Currency adjustment Stockholders' Equity Attributable to Noncontrolling Interest Noncontrolling interests, end of period Noncontrolling interests, beginning of period Noncontrolling interests Other Comprehensive Income, Minimum Pension Liability Net Adjustment, Net of Tax Pension adjustment, net of tax Dividends, Common Stock Dividends Effect of Exchange Rate on Cash and Cash Equivalents Effect of foreign currency translation on cash and cash equivalents Other Expenses Other Stock Issued During Period, Value, Treasury Stock Reissued Issuance of treasury stock Increase (Decrease) in Receivables under Repurchase Agreements Increase (Decrease) in Payables under Repurchase Agreements Proceeds from Issuance of Common Stock Issuance of common shares Net Cash Provided by (Used in) Financing Activities Net cash provided by (used in) financing activities Cash and Cash Equivalents, Period Increase (Decrease) Increase (Decrease) in Securities Loaned Transactions Increase in securities loaned Increase (Decrease) in Accounts Payable and Accrued Liabilities Increase in accrued expenses and other liabilities Cash and cash equivalents (including $219,335 in 2011 and $202,565 in 2010, from VIEs) Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations Financial instruments owned, at fair value, including securities pledged of $14,712,257 and $12,338,728 in 2011 and 2010, respectively: Corporate equity securities (including $181,027 in 2011 and $120,606 in 2010 from VIEs) Corporate debt securities (including $350,507 in 2011 and $462,462 in 2010 from VIEs) Mortgage- and asset-backed securities (including $42,821 in 2011 and $43,355 in 2010 from VIEs) Derivatives (including $13,879 in 2011 and $7,579 in 2010 from VIEs) Investments, at fair value (including $2,762 in 2011 and $15,612 in 2010 from VIEs) Total financial instruments owned, at fair value (including $1,071,914 in 2011 and $1,012,079 in 2010 from VIEs) Other assets (including $241 in 2011 and $370 in 2010 from VIEs) Corporate debt securities (including $272,876 in 2011 and $443,100 in 2010 from VIEs) Brokers, dealers and clearing organizations (including $174,175 in 2011 and $157,134 in 2010 from VIEs) Accrued expenses and other liabilities (including $125,936 in 2011 and $94,402 in 2010 from VIEs) Total liabilities (including $1,063,062 in 2011 and $1,163,465 in 2010 from VIEs) Common stock, $.0001 par value. Authorized 500,000,000 shares; issued 212,148,852 shares in 2011 and 200,301,656 shares in 2010 Transfers and Servicing of Financial Assets [Text Block] Collateralized Transactions Other comprehensive income: Currency translation adjustments Receivables [Abstract] Receivables Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary Net earnings to common shareholders Net Income (Loss) Available to Common Stockholders, Basic Net earnings to common shareholders Net earnings to common shareholders Net Income (Loss) Attributable to Noncontrolling Interest Net earnings to noncontrolling interests Income Taxes Paid, Net Income taxes, net Cash, Cash Equivalents and Short-Term Investments [Abstract] Cash and Cash Equivalents Disclosure [Text Block] Cash, Cash Equivalents and Short-Term Investments Commitments, Contingencies and Guarantees [Abstract] Payments to Acquire Property, Plant, and Equipment Net payments on premises and equipment Other Comprehensive Income (Loss), Net of Tax Total other comprehensive income Adjustments to Additional Paid in Capital, Tax Effect from Share-based Compensation Tax benefit for issuance of share-based awards Retained earnings Retained earnings Noncontrolling interests Noncontrolling interests Treasury stock, at cost Treasury stock, at cost Additional paid-in capital Additional paid-in capital Common stock, par value $0.0001 per share Common stock, par value $0.0001 per share Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total stockholders' equity Total stockholders' equity