KCG 10-K/A 4 Mar 14 2013 FY Annual report (amended) Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Jun. 30, 2013	Feb. 27, 2014	Feb. 27, 2014
			Common Class A [Member]	Common Class B [Member]
Entity Information [Line Items]	'	'	'	'
Entity Registrant Name	'KCG HOLDINGS, INC.	'	'	'
Entity Central Index Key	'0001569391	'	'	'
Document Type	'10-K/A	'	'	'
Document Period End Date	31-Dec-13	'	'	'
Amendment Flag	'true	'	'	'
Document Fiscal Year Focus	'2013	'	'	'
Amendment Description	'We are filing this Amendment No. 1 on Form 10-K/A (the “Amendment”) to the KCG Holdings, Inc. (the “Company”) Annual Report on Form 10-K for the year ended December 31, 2013, as filed with the Securities and Exchange Commission on March 3, 2014 (the “Original Filing”), solely to correct typographical errors in the presentation of earnings and related earnings per share amounts attributable to preferred and common holders contained in Part II, Item 6. Selected Financial Data and Part II, Item 8. Financial Statements and Supplementary Data (Notes to Consolidated Financial Statements (Footnote 2 “Merger of GETCO and Knight”)). The errors related to the reporting of certain earnings per share information that was properly presented on the Consolidated Statements of Operations and in Footnote 19 "Earnings Per Share" but not conformed elsewhere in the Original Filing. This Amendment includes all corrected information, as well as conforming signature pages that were omitted from the Original Filing. The original signature pages were fully executed on March 3, 2014, and were in the Company’s possession at the time of the Original Filing. In addition, the Company is including in this Amendment currently dated certifications from its Chief Executive Officer and Chief Financial Officer as required by Sections 302 and 906 of the Sarbanes-Oxley Act of 2002 as Exhibits 31.1 and 31.2 and Exhibits 32.1 and 32.2, respectively, as well as a new consent of the Company's independent registered accounting firm as Exhibit 23.1. This Form 10-K/A corrects these inadvertent errors. Except as described above, no other changes have been made to the Original Filing, and this Amendment does not otherwise amend, update or change the financial statements or disclosures in the Original Filing.	'	'	'
Document Fiscal Period Focus	'FY	'	'	'
Current Fiscal Year End Date	'--12-31	'	'	'
Entity Filer Category	'Large Accelerated Filer	'	'	'
Entity Common Stock, Shares Outstanding	'	'	125,706,326	0
Entity Well-known Seasoned Issuer	'Yes	'	'	'
Entity Voluntary Filers	'No	'	'	'
Entity Current Reporting Status	'Yes	'	'	'
Entity Public Float	'	$800.60	'	'

CONSOLIDATED_STATEMENTS_OF_FIN

CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (USD $)	Dec. 31, 2013	Dec. 31, 2012
Assets	'	'
Cash and cash equivalents	$674,281,000	$427,631,000
Cash and cash equivalents segregated under federal and other regulations	183,082,000	0
Financial instruments owned, at fair value, including securities pledged to counterparties that had the right to deliver or repledge of $552,242 at December 31, 2013 and $52,261 at December 31, 2012:	'	'
Equities	2,298,785,000	378,933,000
Listed options	339,798,000	92,305,000
Debt securities	83,256,000	183,637,000
Total financial instruments owned, at fair value	2,721,839,000	654,875,000
Collateralized agreements:	'	'
Securities borrowed	1,357,387,000	52,261,000
Receivable from brokers, dealers and clearing organizations	1,257,251,000	142,969,000
Fixed assets and leasehold improvements, less accumulated depreciation and amortization	146,668,000	83,341,000
Investments	122,047,000	248,438,000
Goodwill and Intangible assets, less accumulated amortization	207,754,000	57,035,000
Deferred tax asset, net	173,584,000	4,180,000
Other assets	147,322,000	16,806,000
Total assets	6,991,215,000	1,687,536,000
Financial instruments sold, not yet purchased, at fair value:	'	'
Equities	1,851,006,000	423,740,000
Listed options	252,282,000	69,757,000
Debt securities	57,198,000	19,056,000
Other financial instruments	5,014,000	0
Total financial instruments sold, not yet purchased, at fair value	2,165,500,000	512,553,000
Collateralized financings:	'	'
Securities loaned	733,230,000	0
Financial instruments sold under agreements to repurchase	640,950,000	0
Total collateralized financings	1,374,180,000	0
Payable to brokers, dealers and clearing organizations	474,108,000	24,185,000
Payable to customers	481,041,000	0
Accrued compensation expense	149,430,000	27,728,000
Accrued expenses and other liabilities	172,406,000	118,068,000
Capital lease obligations	10,039,000	24,191,000
Debt	657,259,000	15,000,000
Total liabilities	5,483,963,000	721,725,000
Commitments and Contingent Liabilities (Note 21)	'	'
Redeemable preferred member's equity	0	311,139,000
Equity	'	'
Members' equity	0	654,672,000
Additional paid-in capital	1,306,549,000	0
Retained earnings	209,393,000	0
Treasury stock, at cost; 1,079 shares at December 31, 2013	-11,324,000	0
Accumulated other comprehensive income	1,401,000	0
Total equity	1,507,252,000	654,672,000
Total liabilities, redeemable preferred member's equity and equity	6,991,215,000	1,687,536,000
Common Class A [Member]	'	'
Equity	'	'
Shares authorized: 1,000,000 at December 31, 2013; Shares issued: 123,317 at December 31, 2013; Shares outstanding: 122,238 at December 31, 2013	$1,233,000	$0

CONSOLIDATED_STATEMENTS_OF_FIN1

CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Financial instruments owned, at fair value, securities pledged	$552,242	$52,261
Treasury stock, shares	1,079,000	0
Common Class A [Member]	'	'
Class A common stock Shares authorized	1,000,000,000	0
Class A common stock, Shares issued	123,317,000	0
Class A common stock, Shares outstanding	122,238,000	0

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues	'	'	'
Trading revenues, net	$628,304	$421,063	$611,845
Commissions and fees	275,474	105,518	284,620
Interest, net	-537	-2,357	-1,211
Investment income and other, net	116,930	27,010	20,194
Total revenues	1,020,171	551,234	915,448
Expenses	'	'	'
Employee compensation and benefits	349,192	157,855	241,753
Execution and clearance fees	246,414	185,790	289,025
Communications and data processing	123,552	90,623	87,116
Interest	44,785	2,665	1,299
Depreciation and amortization	55,570	34,938	45,675
Payments for order flow	35,711	2,964	3,299
Professional fees	46,662	14,072	17,142
Occupancy and equipment rentals	24,812	12,804	9,903
Business development	4,609	23	108
Writedown of capitalized debt costs	13,209	0	0
Writedown of assets and lease loss accrual	14,748	0	0
Other	43,094	23,073	26,587
Total expenses	1,002,358	524,807	721,907
Income from continuing operations before income taxes	17,813	26,427	193,541
Income tax (benefit) expense	-102,195	10,276	30,841
Income from continuing operations, net of tax	120,008	16,151	162,700
Income from discontinued operations, net of tax	80	0	0
Net income	120,088	16,151	162,700
Net (loss) income allocated to preferred and participating units	-21,565	1,092	12,510
Net income attributable to common shareholders	$141,653	$15,059	$150,190
Basic earnings per share from continuing operations (in dollars per share)	$1.77	$0.31	$2.96
Diluted earnings per share from continuing operations (in dollars per share)	$1.75	$0.31	$2.96
Basic loss per share from discontinued operations (in dollars per share)	$0	$0	$0
Diluted loss per share from discontinued operations (in dollars per share)	$0	$0	$0
Basic earnings per share (in dollars per share)	$1.77	$0.31	$2.96
Diluted earnings (loss) per share (in dollars per share)	$1.75	$0.31	$2.96
Shares used in computation of basic earnings (loss) per share (in shares)	80,143	48,970	50,688
Shares used in computation of diluted earnings (loss) per share (in shares)	81,015	48,970	50,688

CONSOLIDATED_STATEMENTS_OF_CHA

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $)	Total	Redeemable preferred members' equity [Member}	Members Equity [Member]	Unrecognized Compensation [Member]	Common Class A [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated other comprehensive income (loss) [Member]	Total Equity [Member]
In Thousands, unless otherwise specified
Balance at Dec. 31, 2010	'	$338,158	$570,434	($38,023)	$0	$0	$0	$0	$0	$532,411
Balance (in shares) at Dec. 31, 2010	'	'	'	'	0	'	'	0	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'	'	'
Contributions	'	'	48,789	-5,745	'	'	'	'	'	43,044
Repurchase of Membership interests	'	'	-15,410	'	'	'	'	'	'	-15,410
Distributions	'	-23,668	-99,749	'	'	'	'	'	'	-99,749
Net (loss) income	162,700	'	162,700	'	'	'	'	'	'	162,700
Balance at Dec. 31, 2011	'	314,490	666,764	-43,768	0	0	0	0	0	622,996
Balance (in shares) at Dec. 31, 2011	'	'	'	'	0	'	'	0	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'	'	'
Contributions	'	'	12,695	24,829	'	'	'	'	'	37,524
Repurchase of Membership interests	'	'	-111,525	'	'	'	'	'	'	-111,525
Distributions	'	-3,351	-24,793	'	'	'	'	'	'	-24,793
Net (loss) income	16,151	'	16,151	'	'	'	'	'	114,319	130,470
Balance at Dec. 31, 2012	654,672	311,139	559,292	-18,939	0	0	0	0	114,319	654,672
Balance (in shares) at Dec. 31, 2012	'	'	'	'	0	'	'	0	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'	'	'
Contributions	'	'	11,339	18,939	'	'	'	'	'	30,278
Repurchase of Membership interests	'	'	-5,833	'	'	'	'	'	'	-5,833
Distributions	'	'	-2,054	'	'	'	'	'	'	-2,054
Net (loss) income	'	'	-89,305	'	'	'	'	'	'	-89,305
Modification of redemption value	'	-21,565	21,565	'	'	'	'	'	'	21,565
Unrealized gain on available for sale securities	'	'	'	'	'	'	'	'	4,550	4,550
Cumulative translation adjustment	'	'	'	'	'	'	'	'	-403	-403
Balance at Jun. 30, 2013	'	289,574	495,004	0	0	0	0	0	118,466	613,470
Balance (in shares) at Jun. 30, 2013	'	'	'	'	0	'	'	0	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'	'	'
Net (loss) income	'	'	'	'	'	'	209,393	'	'	209,393
Gain on investment in Knight Capital Group, Inc.	'	'	'	'	'	'	'	'	9,103	9,103
Reclassification of investment in Knight out of other comprehensive income	'	'	'	'	'	'	'	'	-127,972	-127,972
Equity issued to General Atlantic	'	'	55,000	'	'	'	'	'	'	55,000
Exchange of membership interest for shares of KCG Class A Common Stock (in shares)	'	'	'	'	75,868	'	'	'	'	'
Exchange of membership interests for shares of KCG Class A Common Stock	'	-289,574	-550,004	'	759	754,417	'	'	'	205,172
Exchange of membership interests for warrants to purchase KCG Class A Common Stock	'	'	'	'	'	74,896	'	'	'	74,896
Issuance of KCG Class A Common Stock to Knight stockholders	'	'	'	'	419	453,419	'	'	'	453,838
Issuance of KCG Class A Common Stock to Knight stockholders (in shares)	'	'	'	'	41,889	'	'	'	'	'
Change in estimated distribution payable to members	'	'	'	'	'	1,757	'	'	'	1,757
KCG Class A Common Stock repurchased	'	'	'	'	'	'	'	-11,324	'	-11,324
KCG Class A Common Stock repurchased (in shares)	'	'	'	'	'	'	'	-1,079	'	'
Stock-based compensation	'	'	'	'	55	22,060	'	'	'	22,115
Stock-based compensation (in shares)	'	'	'	'	5,560	'	'	'	'	'
Unrealized gain on available for sale securities	'	'	'	'	'	'	'	'	36	36
Cumulative translation adjustment	'	'	'	'	'	'	'	'	1,768	1,768
Balance at Dec. 31, 2013	'	$0	$0	$0	$1,233	$1,306,549	$209,393	($11,324)	$1,401	$1,507,252
Balance (in shares) at Dec. 31, 2013	'	'	'	'	123,317	'	'	1,079	'	'

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$120,088	$16,151	$162,700
Unrealized (loss) gain on available for sale securities, net of tax	-114,283	114,319	0
Cumulative translation adjustment, net of tax	1,365	0	0
Comprehensive income	$7,170	$130,470	$162,700

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities	'	'	'
Net income	$120,088	$16,151	$162,700
Income from discontinued operations, net of tax	80	0	0
Income from continuing operations, net of tax	120,008	16,151	162,700
Adjustments to reconcile income from continuing operations, net of tax to net cash provided by (used in) operating activities	'	'	'
Non-cash gain on Knight Common Stock	-127,972	0	0
Deferred tax benefit	-103,499	0	0
Depreciation and amortization	55,570	34,938	45,675
Stock and unit-based compensation	64,286	12,320	43,044
Unrealized gain (loss) on investments	2,627	-25,754	-22,750
Writedown of assets and lease loss accrual	14,748	0	0
Writedown and amortization of debt offering costs	17,332	276	0
Deferred rent	58	0	0
Operating activities from discontinued operations	6,952	0	0
(Increase) decrease in operating assets	'	'	'
Cash and securities segregated under federal and other regulations	19,963	0	0
Financial instruments owned, at fair value	-129,035	-414,537	-140,414
Securities borrowed	-146,145	-30,679	18,932
Receivable from brokers, dealers and clearing organizations	252,266	36,439	93,940
Other assets	24,703	1,332	-2,922
(Decrease) increase in operating liabilities	'	'	'
Financial instruments sold, not yet purchased, at fair value	139,951	0	-50,917
Securities loaned	106,339	0	0
Financial instruments sold under agreements to repurchase	95,950	372,023	0
Payable to brokers, dealers and clearing organizations	-185,992	-34,752	50,313
Payable to customers	-46,877	0	0
Accrued compensation expense	24,441	-18,494	8,209
Accrued expenses and other liabilities	-64,470	-13,779	4,472
Net cash provided by (used in) operating activities	141,204	-64,516	210,282
Cash flows from investing activities	'	'	'
Acquisition of trading rights	0	0	-30,828
Purchase of acquisition	0	0	-10,945
Proceeds and distributions from investments	3,251	72,196	1,047
Purchases of investments	-27,703	-31,389	-62,790
Purchases of investments	-158	-87,308	-6,118
Investing activities from discontinued operations	12,963	0	0
Net cash provided by (used in) investing activities	582,892	-46,501	-109,634
Cash flows from financing activities	'	'	'
Proceeds from issuance of Credit Agreement	535,000	0	0
Partial repayment of Credit Agreement	-300,000	0	0
Proceeds from issuance of Senior Secured Notes	305,000	0	0
Proceeds from issuance of notes payable	0	0	15,000
Repayment of notes payable	-15,000	'	'
Payment of debt issuance cost	-34,592	-1,375	0
Issuance of equity to General Atlantic	55,000	0	0
Payment to former Knight Capital Group, Inc. stockholders	-720,000	0	0
Repayment of Knight Convertible Notes	-257,741	0	0
Funding of collateral account for Knight Convertible Notes	-117,259	0	0
Payment out of collateral account for Knight Convertible Notes	117,259	0	0
Borrowings under secured credit facility	25,000	88,750	0
Repayment of secured credit facility	-25,000	-88,750	0
Borrowings under capital lease obligations	0	15,558	15,786
Principal payments on capital lease obligations	-14,152	-20,990	-12,979
Members' distributions	-21,002	-37,061	-122,227
Repurchase of members' interest	0	-25,173	-2,564
Cost of common stock repurchased	-11,324	0	0
Net cash used in financing activities	-478,811	-69,041	-106,984
Effect of exchange rate changes on cash and cash equivalents	1,365	0	0
Increase (decrease) in cash and cash equivalents	246,650	-180,058	-6,336
Cash and cash equivalents at beginning of period	427,631	607,689	614,025
Cash and cash equivalents at end of period	674,281	427,631	607,689
Supplemental disclosure of cash flow information:	'	'	'
Cash paid for interest	56,227	8,084	3,641
Cash paid for income taxes	10,198	21,789	31,114
Knight Capital Group [Member]	'	'	'
Cash flows from investing activities	'	'	'
Cash acquired upon acquisition of Knight Capital Group, Inc.	509,133	0	0
Urban Financial America [Member]	'	'	'
Cash flows from investing activities	'	'	'
Cash received from sale of Urban Financial of America, LLC	$85,406	$0	$0

Organization_and_Description_o

Organization and Description of the Business	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Organization and Description of the Business	'
	Organization and Description of the Business
	On December 19, 2012, Knight Capital Group, Inc.(“Knight”), GETCO Holding Company, LLC (“GETCO”) and an affiliate of GETCO entered into an agreement and plan of merger (as amended and restated on April 15, 2013 the “Merger Agreement”) for a series of strategic business combinations (the “Mergers”). The Mergers were approved by the respective stockholders and unitholders of both companies at special meetings held on June 25, 2013, and the Mergers were completed on July 1, 2013. As a result of the Mergers, Knight and GETCO each became a wholly-owned subsidiary of KCG Holdings, Inc. (collectively with its subsidiaries, “KCG” or the “Company”).
	The Mergers took place in order to combine the businesses, intellectual capital and resources of the two companies to more successfully compete in the highly regulated and technologically advanced marketplace and to allow for further diversification of each company's revenues from principal and agency trading across asset classes and regions. The Mergers were treated as a purchase of Knight by GETCO for accounting and financial reporting purposes. As a result, the financial results for the year ended December 31, 2013 comprise the results of GETCO only for the six months ended June 30, 2013 and the results of KCG (the combined Knight and GETCO) for the six months ended December 31, 2013. All periods prior to 2013 reflect solely the results and financial condition of GETCO.
	KCG is a leading independent securities firm offering clients a range of services designed to address trading needs across asset classes, product types and time zones. The Company combines advanced technology with specialized client service across market making, agency execution and trading venues and also engages in principal trading via exchange-based electronic market making. KCG has multiple access points to trade global equities, options, fixed income, currencies and commodities via voice or automated execution.
	As of December 31, 2013, the Company's operating segments comprised the following: (i) Market Making; (ii) Global Execution Services; and (iii) Corporate and Other.
	Market Making
	The Market Making segment principally consists of market making in the cash, futures and options markets across global equities, options, fixed income, foreign currencies and commodities. As a market maker, the Company commits capital on a principal basis by offering to buy securities from, or sell securities to, broker dealers, institutions and banks. Principal trading in the Market Making segment primarily consists of direct-to-client and non-client exchange-based electronic market making, including trade executions conducted as an equities Designated Market Maker (“DMM”) on the New York Stock Exchange ("NYSE") and NYSE Amex Equities ("NYSE Amex"). The Company is an active participant on all major global equity and futures exchanges and also trades on substantially all domestic electronic options exchanges. As a complement to electronic market making, the Company’s cash trading business handles specialized orders and also transacts on the OTC Bulletin Board, marketplaces operated by the OTC Markets Group Inc. and the Alternative Investment Market (“AIM”) of the London Stock Exchange.
	Global Execution Services
	The Global Execution Services segment comprises agency execution services and trading venues, offering trading in global equities, options, foreign exchange, fixed income and futures to institutions, banks and broker dealers. The Company generally earns commissions as an agent between principals to transactions that are executed within this segment, however, the Company will commit capital on behalf of clients as needed. Agency-based, execution-only trading in the segment primarily consists of self-directed trading in global equities through a suite of algorithms or via the Company's execution management system; institutional high touch sales traders executing program, block and riskless principal trades in global equities and exchange traded funds ("ETFs"); an institutional spot foreign exchange electronic communication network ("ECN"); a fixed income ECN that also offers trading applications; an alternative trading system ("ATS") for global equities; and futures execution and clearing through a futures commission merchant ("FCM").
	Corporate and Other
	The Corporate and Other segment invests principally in strategic financial services-oriented opportunities; allocates, deploys and monitors all capital; and maintains corporate overhead expenses and all other income and expenses that are not attributable to the other segments. The Corporate and Other segment also contains functions that support the Company’s other segments such as self-clearing services, including stock lending activities.
	Discontinued Operations
	Management of the Company from time to time conducts a strategic review of its businesses and evaluates their potential value in the marketplace relative to their current and expected returns. To the extent management and the Company's Board of Directors determine a business may return a higher value to stockholders through a divestiture, or is no longer core to the Company's strategy, management may pursue a sale process.
	In July 2013, KCG entered into an agreement to sell to an investor group Urban Financial of America, LLC, formerly known as Urban Financial Group, Inc. (“Urban”), the reverse mortgage origination and securitization business that was previously owned by Knight. The transaction was completed in the fourth quarter of 2013, and the results of Urban's operations have been reported in Income from discontinued operations, net of tax on the Consolidated Statements of Operations for the year ended December 31, 2013. See Footnote 4 "Discontinued Operations" for further discussion.

Merger_of_GETCO_and_Knight

Merger of GETCO and Knight	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Merger With GETCO and Knight	'
	Merger of GETCO and Knight
	Background
	Pursuant to the Merger Agreement, upon completion of the Mergers on July 1, 2013, subject to proration and certain specified exceptions, each outstanding share of Knight Class A common stock, par value $0.01 per share (“Knight Common Stock”) was converted into the right to elect to receive either $3.75 per share in cash or one third of a share of KCG Class A common stock, par value $0.01 per share (“KCG Class A Common Stock”). Pursuant to the proration procedures provided in the Merger Agreement and taking into account the waiver by Jefferies LLC (Knight's largest stockholder before the Mergers) of its right to receive cash consideration with respect to certain of its shares, former Knight stockholders eligible for election received cash payments aggregating $720.0 million and 41.9 million shares of KCG Class A Common Stock.
	Upon completion of the Mergers, GETCO unitholders received, in aggregate, 75.9 million shares of KCG Class A Common Stock and 24.3 million warrants to acquire shares of KCG Class A Common Stock. The warrants comprise 8.1 million Class A warrants, having a $12.00 exercise price and exercisable for a four-year term; 8.1 million Class B warrants, having a $13.50 exercise price and exercisable for a five-year term; and 8.1 million Class C warrants, having a $15.00 exercise price and exercisable for a six-year term (collectively the “KCG Warrants”).
	After taking into account the election results and the shares of KCG Class A Common Stock issued to former unitholders of GETCO and former stockholders of Knight, 116.8 million shares (including unvested restricted stock units ("RSUs")) of KCG Class A Common Stock were outstanding as of July 1, 2013.
	Accounting treatment of the Mergers
	The Mergers are accounted for as a purchase of Knight by GETCO under accounting principles generally accepted in the United States of America ("GAAP") based on, among other factors, the controlling ownership position of the former GETCO unitholders as of the closing of the Mergers. Under the purchase method of accounting, the assets and liabilities of Knight as of July 1, 2013 were recorded at their respective fair values and added to the carrying value of GETCO's existing assets and liabilities. The reported financial condition and results of operations of KCG for the periods following the Mergers reflect Knight's and GETCO's balances and reflect the impact of purchase accounting adjustments, including revised amortization and depreciation expense for acquired assets. As GETCO is the accounting acquirer, the financial results for KCG for the year ended December 31, 2013 comprise the results of KCG for the six months ended December 31, 2013 and the results of GETCO only for the six months ended June 30, 2013. All periods prior to 2013 comprise solely the results of GETCO.
	Prior to the Mergers, GETCO treated its investment in Knight as an available-for-sale security, which it recorded at fair value, with any gains or losses recorded in other comprehensive income as a component of equity. Upon completion of the Mergers the Company reversed the cumulative gain that it had recorded in other comprehensive income within equity and recognized a gain of $128.0 million in Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013.
	All GETCO earnings per share and unit share outstanding amounts in these financial statements have been calculated as if the conversion of GETCO units to KCG Class A Common Stock took place on January 1, 2011, at the exchange ratio as defined in the Merger Agreement. See Footnote 19 "Earnings Per Share" for further discussion.
	Purchase price and goodwill
	The Knight acquisition was accounted for using the acquisition method of accounting. The aggregate purchase price of $1.37 billion was determined as the sum of the fair value of KCG shares issued to former Knight stockholders at closing; the fair value of Knight employee stock based awards attributable to periods prior to closing; and the fair value of the Knight Common Stock owned by GETCO and its subsidiaries immediately prior to the Mergers (and subsequently canceled in conjunction with the Mergers).
	The purchase price has been allocated to the assets acquired and liabilities assumed using their estimated fair values at July 1, 2013, the closing date of the Mergers. The Company has not yet completed all of its analysis to finalize the allocation of the purchase price to the Knight acquired assets and liabilities. The allocation of the purchase price may be modified over the measurement period, as more information is obtained about the fair values of assets acquired and liabilities assumed.
	Tax treatment of the Mergers
	The Company believes that the Mergers will be treated as a transaction described in Section 351 of the Internal Revenue Code, and both Knight and GETCO have received tax opinions from external legal counsel to that effect. Knight’s tax basis in its assets and liabilities therefore generally carries over to the Company following the Mergers. Upon completion of the Mergers, the Company became a corporation subject to U.S. corporate income taxes and, following the Mergers, the Company recorded deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial reporting and tax bases of assets and liabilities. The Company measures deferred taxes using the enacted tax rates and laws that will be in effect when such temporary differences are expected to reverse.
	The Company recorded net deferred tax assets of $62.3 million with respect to recording Knight’s assets and liabilities under the purchase method of accounting as described above as well as recording the value of a tax net operating loss ("NOL”) carryforwards and other tax attributes acquired as a result of the Mergers, as described in Footnote 16 “Income Taxes”.
	The following table reflects the preliminary allocation of the purchase price to the assets acquired and liabilities assumed at the acquisition date (in thousands):
	Identifiable Net Assets
	Cash and cash equivalents				$	509,133
	Cash and securities segregated under federal and other regulations				203,045
	Financial instruments owned				1,937,929
	Securities borrowed				1,158,981
	Receivable from brokers, dealers and clearing organizations				1,369,474
	Fixed assets and leasehold improvements				80,280
	Investments				106,353
	Intangible assets				155,425
	Assets within discontinued operations				5,607,063
	Deferred tax asset, net				62,329
	Other assets				141,617
	Total Assets				$	11,331,629
	Financial instruments sold, not yet purchased				$	1,512,983
	Collateralized financings				1,166,211
	Payable to brokers, dealers and clearing organizations				635,914
	Payable to customers				527,918
	Accrued compensation expense				107,409
	Accrued expenses and other liabilities				126,507
	Liabilities within discontinued operations				5,518,168
	Long-term debt				375,000
	Total Liabilities				$	9,970,110
	Total identified assets acquired, net of assumed liabilities				1,361,519
	Goodwill				11,615
	Total Purchase Price				$	1,373,134
	Goodwill has been primarily assigned to the Market Making segment of the Company. None of the goodwill is expected to be deductible for tax purposes; however, as described in Tax treatment of the Mergers above, Knight’s tax basis in its assets, including certain goodwill, has carried over to the Company as a result of the Mergers.
	Amounts preliminarily allocated to intangible assets and goodwill, and the amortization period for intangible assets with finite useful lives, were as follows (dollars in thousands):
							Amortization
			Amount				Years
	Technology		$	110,504			5 years
	Customer relationships		35,000				9 - 11 years
	Trade names		4,000				10 years
	Trading rights (1)		5,921				7 years
	Intangible assets		155,425
	Goodwill		11,615
	Total		$	167,040
	(1) Trading rights include both assets with a finite useful life and assets with an indefinite useful life. The 7 years amortization period only applies to assets with a finite useful life.
	The Company recorded $38.9 million of costs related to the Mergers for the year ended December 31, 2013.
	Pro forma results
	Included in KCG results for the year ended December 31, 2013 are results from the businesses acquired as a result of the Mergers as follows (in thousands):
		Year ended December 31,
		2013
	Revenues	$	486,119
	Income from continuing operations, before income taxes	54,070
	The following pro forma results are based on adding the pre-tax historical results of GETCO and Knight, and adjusting primarily for amortization of intangibles acquired in the Mergers, debt raised in conjunction with the Mergers and income taxes as if the Company was subject to U.S. corporate income taxes for all periods presented. The pro forma data assumes that no payments were made on the First Lien Credit Facility (as later defined) except those prescribed in the Credit Agreements (as later defined), that all GETCO units have been converted to KCG Class A Common Stock on January 1, 2012, and excludes any gain recognized on Knight Common Stock. The pro forma disclosures do not include adjustments to reflect the Company's operating costs or expected differences in the way funds generated by the Company are invested. The pro forma data is intended for informational purposes and is not indicative of the future results of operations.
			Year ended December 31, 2013							Year ended December 31, 2012
			Reported				Pro Forma (unaudited)			Reported		Pro Forma (unaudited)
		(in thousands, except per share amounts)
Revenue		$	1,020,171			$	1,421,566		$	551,234	$	1,020,334
Net income from continuing operations		120,008				(69,414		)	16,151		(286,656		)
Net income		120,088				(98,394		)	16,151		(355,130		)
Diluted earnings (loss) per common share from continuing operations		$	1.75			$	(0.86	)	$	0.31	$	(5.85	)
Diluted earnings (loss) per common share		$	1.75			$	(1.21	)	$	0.31	$	(7.25	)

Significant_Accounting_Policie

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Significant Accounting Policies	'
	Significant Accounting Policies
	Basis of consolidation and form of presentation
	The Consolidated Financial Statements, prepared in conformity with GAAP, include the accounts of the Company and its subsidiaries. All significant intercompany transactions and balances have been eliminated.
	Certain reclassifications have been made to the prior periods’ Consolidated Financial Statements in order to conform to the current period presentation. Such reclassifications are immaterial to both current and all previously issued financial statements taken as a whole and have no effect on previously reported Consolidated Net income.
	Cash and cash equivalents
	Cash and cash equivalents include money market accounts, which are payable on demand, and short-term investments with an original maturity of less than 90 days. The carrying amount of such cash equivalents approximates their fair value due to the short-term nature of these instruments.
	Cash and securities segregated under federal and other regulations
	The Company maintains custody of customer funds and is obligated by rules and regulations mandated by the U.S. Securities and Exchange Commission (“SEC”) and the Commodities Futures Trading Commission (“CFTC”) to segregate or set aside cash and/or qualified securities to satisfy these regulations, which have been promulgated to protect customer assets. The amounts recognized as Cash and securities segregated under federal and other regulations approximate fair value.
	Market making, sales, trading and execution activities
	Financial instruments owned and Financial instruments sold, not yet purchased, relate to market making and trading activities, include listed and other equity securities, listed equity options and fixed income securities which are recorded on a trade date basis and carried at fair value. Trading revenues, net, which comprises trading gains, net of trading losses, are also recorded on a trade date basis.
	Commissions, which includes commission equivalents earned on institutional client orders and commissions on futures transactions, and related expenses are also recorded on a trade date basis. Commissions earned by the Company’s FCM are recorded net of any commissions paid to independent brokers and are recognized on a half-turn basis.
	The Company’s third party clearing agreements call for payment or receipt of interest income, net of transaction-related interest charged by such clearing brokers, for facilitating the settlement and financing of securities transactions. Interest income and interest expense which have been netted within Interest, net on the Consolidated Statements of Operations are as follows (in thousands):
		For the year ended December 31,
		2013			2012			2011
	Interest Income	$	10,187		$	3,070		$	1,131
	Interest Expense	(10,724		)	(5,427		)	(2,342		)
	Interest, net	$	(537	)	$	(2,357	)	$	(1,211	)
	Dividend income relating to securities owned and dividend expense relating to securities sold, not yet purchased, derived primarily from the Company’s market making activities are included as a component of Trading revenue, net on the Consolidated Statements of Operations. Trading revenue, net includes dividend income and expense as follows (in thousands):
		For the year ended December 31,
		2013			2012			2011
	Dividend Income	$	26,237		$	2,253		$	4,700
	Dividend Expense	$	(21,630	)	$	(1,599	)	$	(1,512	)
	Payments for order flow represent payments to broker dealer clients, in the normal course of business, for directing their order flow in U.S. equities and options to the Company.
	Fair value of financial instruments
	The Company values its financial instruments using a hierarchy of fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value.
	The fair value hierarchy can be summarized as follows:
	•	Level 1—Valuations based on quoted prices in active markets for identical assets or liabilities that the Company has the ability to access. Since valuations are based on quoted prices that are readily and regularly available in an active market, valuation of these products does not entail a significant degree of judgment.
	•	Level 2—Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly.
	•	Level 3—Valuations based on inputs that are unobservable and significant to the overall fair value measurement.
	Changes in fair value are recognized in earnings each period for financial instruments that are carried at fair value. See Footnote 6 “Fair Value of Financial Instruments” for a description of valuation methodologies applied to the classes of financial instruments at fair value.
	Collateralized agreements and financings
	Collateralized agreements consist of securities borrowed and collateralized financings include securities loaned and financial instruments sold under agreements to repurchase.
	•	Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral advanced or received. Securities borrowed transactions facilitate the securities settlement process and require the Company to deposit cash or other collateral with the lender. Securities loaned transactions help finance the Company’s securities inventory whereby the Company lends stock to counterparties in exchange for the receipt of cash or other collateral from the borrower. In these transactions, the Company receives or lends cash or other collateral in an amount generally in excess of the market value of the applicable securities borrowed or loaned. The Company monitors the market value of securities borrowed or loaned on a daily basis, and obtains additional collateral or refunds excess collateral as necessary.
	•	Financial instruments sold under agreements to repurchase are used to finance inventories of securities and other financial instruments and are recorded at their contractual amount. The Company has entered into bilateral and tri-party term and overnight repurchase agreements which bear interest at negotiated rates. The Company receives cash and makes delivery of financial instruments to a custodian who monitors the market value of these instruments on a daily basis. The market value of the instruments delivered must be equal to or in excess of the principal amount loaned under the repurchase agreements plus the agreed upon margin requirement. The custodian may request additional collateral, if appropriate.
	The Company’s securities borrowed, securities loaned and financial instruments sold under agreements to repurchase are recorded at amounts that approximate fair value. These items are recorded based upon their contractual terms and are not materially sensitive to shifts in interest rates because they are short-term in nature and are fully collateralized. These items would be categorized as Level 2 in the fair value hierarchy if they were required to be recorded at fair value.
	Investments
	Investments primarily comprise strategic noncontrolling equity ownership interests in financial services-related businesses and are held by the Company's non-broker dealer subsidiaries. These strategic investments are accounted for under either the equity method, at fair value or at cost. The equity method of accounting is used when the Company has significant influence. Strategic investments are held at cost, less impairment if any, when the investment does not have a readily determined fair value, and the Company is not considered to exert significant influence on operating and financial policies of the investee.
	Prior to the Mergers, GETCO had a strategic investment in Knight which was classified as available for sale and held at fair value with any unrealized gains or losses recorded in Other comprehensive income or loss. As a result of the Mergers, the Company recognized a non-cash gain of $128.0 million on its investment in Knight Common Stock, which it recorded within Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013 and reversed any previous unrealized gains out of Other comprehensive income.
	Strategic investments are reviewed on an ongoing basis to ensure that the carrying values of the investments have not been impaired. If the Company determines that an impairment loss on a strategic investment has occurred due to a decline in fair value or other market conditions, the investment is written down to its estimated fair value.
	The Company maintains a non-qualified deferred compensation plan for certain employees and directors. This plan provides a return to the participants based upon the performance of various investments. In order to hedge its liability under this plan, the Company generally acquires the underlying investments and holds such investments until the deferred compensation liabilities are satisfied. Changes in value of such investments are recorded in Investment income and other, net, with a corresponding charge or credit to Employee compensation and benefits on the Consolidated Statements of Operations. Deferred compensation investments primarily consist of mutual funds, which are accounted for at fair value.
	Goodwill and intangible assets
	The Company tests goodwill and intangible assets with an indefinite useful life for impairment annually or when an event occurs or circumstances change that signifies the existence of an impairment. The Company capitalizes certain costs associated with the acquisition or development of internal-use software and amortizes the software over its estimated useful life of three years, commencing at the time the software is placed in service. The Company amortizes intangible assets with a finite life on a straight line basis over their estimated useful lives and tests for recoverability whenever events indicate that the carrying amounts may not be recoverable.
	Payable to customers
	Payable to customers arise primarily from futures transactions and include amounts due on cash and margin transactions. Due to their short-term nature, such amounts approximate fair value.
	Treasury stock
	The Company records its purchases of treasury stock at cost as a separate component of stockholders’ equity. The Company may obtain treasury stock through purchases in the open market or through privately negotiated transactions. Certain treasury stock repurchases represent shares of KCG Class A Common Stock repurchased in satisfaction of tax withholding obligations upon vesting of restricted awards. The Company may re-issue treasury stock, at average cost, for the acquisition of new businesses or, in certain instances, as inducement grants to new hires.
	Foreign currency translation and foreign currency forward contracts
	The Company has foreign subsidiaries that do not utilize the U.S. dollar as their functional currency.
	Assets and liabilities of the foreign subsidiaries having non-U.S. dollar functional currencies are translated at exchange rates at the end of a period. Revenues and expenses are translated at average exchange rates during the period. Gains and losses resulting from translating foreign currency financial statements into U.S. dollars are included in Accumulated other comprehensive income on the Consolidated Statements of Financial Condition and Cumulative translation adjustment on the Consolidated Statements of Comprehensive Income. Gains or losses resulting from foreign currency transactions are included in Investment income and other, net on the Company’s Consolidated Statements of Operations. For the years ended December 31, 2013, 2012, and 2011 the Company recorded a loss of $4.1 million, a gain of $0.2 million and a loss of $2.4 million, respectively.
	The Company seeks to reduce the impact of fluctuations in foreign exchange rates on its net investment in certain non-U.S. operations through the use of foreign currency forward contracts. For foreign currency forward contracts designated as hedges, the Company assesses its risk management objectives and strategy, including identification of the hedging instrument, the hedged item and the risk exposure and how effectiveness is to be assessed prospectively and retrospectively. The effectiveness of the hedge is assessed based on the overall changes in the fair value of the forward contracts. For qualifying net investment hedges, any gains or losses, to the extent effective, are included in Accumulated other comprehensive income or loss on the Consolidated Statements of Financial Condition and the Consolidated Statements of Comprehensive Income. The ineffective portion, if any, is recorded in Investment income and other, net on the Consolidated Statements of Operations.
	Stock and unit based compensation
	Stock and unit based compensation is measured based on the grant date fair value of the awards. These costs are amortized over the requisite service period, which is typically the vesting period. Expected forfeitures are considered in determining stock-based employee compensation expense.
	The Company applies a non-substantive vesting period approach for stock-based awards related to KCG Class A Common Stock whereby the expense is accelerated for those employees and directors that receive options, stock appreciation rights ("SARs") and RSUs and are eligible to retire prior to the vesting of such awards.
	Soft dollar expense
	Under a commission management program, the Company allows institutional clients to allocate a portion of their gross commissions to pay for research and other services provided by third parties. As the Company acts as an agent in these transactions, it records such expenses on a net basis within Commissions and fees on the Consolidated Statements of Operations.
	Depreciation, amortization and occupancy
	Fixed assets are depreciated on a straight-line basis over their estimated useful lives of three to seven years. Leasehold improvements are being amortized on a straight-line basis over the shorter of the term of the related office lease or the expected useful life of the assets.The Company reviews fixed assets and leasehold improvements for impairment whenever events or changes in circumstances indicate that the related carrying amounts may not be recoverable.
	The Company recognizes rent expense under operating leases with fixed rent escalations, lease incentives and free rent periods on a straight-line basis over the lease term beginning on the date the Company takes possession of or controls the use of the space, including during free rent periods.
	Lease loss accrual
	The Company’s policy is to identify excess real estate capacity and where applicable, accrue for related future costs, net of estimated sub-lease income upon the date the Company ceases to use the excess real estate. In the event the Company is able to sublease the excess real estate after recording a lease loss, such accrual is adjusted to the extent the actual terms of sub-leased property differ from the assumptions used in the calculation of the accrual. In the event that the Company concludes that previously determined excess real estate is needed for the Company’s use, such lease loss accrual is adjusted accordingly.
	Income taxes
	Prior to the Mergers, GETCO and the majority of its subsidiaries were treated as partnerships or disregarded entities for U.S. income tax purposes and, accordingly, were not subject to federal income taxes. Instead, the former GETCO members were liable for federal income taxes on their proportionate share of taxable income. Upon completion of the Mergers, the Company became a corporation subject to U.S. corporate income taxes and, following the Mergers, the Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial reporting and tax bases of assets and liabilities and measures them using the enacted tax rates and laws that will be in effect when such differences are expected to reverse. The Company evaluates the recoverability of future tax deductions by assessing the adequacy of future expected taxable income from all sources, including reversal of temporary differences and forecasted operating earnings.
	Use of estimates
The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates.
Recently adopted accounting guidance
In December 2011, the Financial Accounting Standards Board (“FASB”) issued an Accounting Standard Update (“ASU”) that requires additional disclosures about financial assets and liabilities that are subject to netting arrangements. Under the ASU, financial assets and liabilities must be disclosed at their respective gross asset and liability amounts, the amounts offset on the balance sheet and a description of the respective netting agreements. The new disclosures were required for reporting periods beginning on or after January 1, 2013, and are to be applied retrospectively. Other than requiring additional disclosures, the adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements.
In February 2013, the FASB issued an ASU that requires additional disclosure requirements for items reclassified out of accumulated other comprehensive income. This new guidance requires entities to present either on the face of the income statement or in the notes to the financial statements the effects on the specific line items of the income statement for amounts reclassified out of accumulated other comprehensive income. This ASU was effective for reporting periods beginning after December 15, 2012. Other than additional disclosure requirements, the adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements.
Recent accounting guidance to be adopted in future periods
In March 2013, the FASB issued an ASU concerning the parent's accounting for the cumulative translation adjustment upon derecognition of certain subsidiaries or groups of assets within a foreign entity or of an investment in a foreign entity. This ASU provides for the release of the cumulative translation adjustment into net income when a parent sells a part or all of its investment within a foreign entity, no longer holds a controlling interest in an investment in a foreign entity or obtains control of an investment in a foreign entity that was previously recognized as an equity method investment. This ASU is effective for reporting periods beginning after December 15, 2013, however early adoption is permitted. The adoption of this ASU will not have an impact on the Company's Consolidated Financial Statements.
In July 2013, the FASB issued an ASU to clarify the financial statement presentation of an unrecognized tax benefit when a NOL carryforward, a similar tax loss, or a tax credit carryforward exists. This ASU requires entities to present an unrecognized tax benefit as a reduction of a deferred tax asset for a NOL carryforward whenever the NOL or tax credit carryforward would be available to reduce the additional taxable income or tax due if the tax position is disallowed. The ASU is required for reporting periods beginning after December 15, 2013. Upon adoption, entities are required to apply the provisions of the ASU prospectively for all unrecognized tax benefits that exist at the adoption date, however, the ASU also indicates that retrospective application is permitted. The adoption of this ASU will not have an impact on the Company's Consolidated Financial Statements.

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Discontinued Operations	'
	Discontinued Operations
	As part of the Mergers, KCG acquired certain assets and liabilities from Knight related to discontinued operations. The assets and liabilities were not considered part of the Company's continuing operations, and, therefore, the results have been included in Income from discontinued operations, net of tax within the Consolidated Statements of Operations for the year ended December 31, 2013. In addition, in July 2013, the Company entered into an agreement to sell to an investor group Urban, the reverse mortgage origination and securitization business that was previously owned by Knight. The transaction was completed in the fourth quarter of 2013, and, as a result, the results of Urban's operations have also been included in Income from discontinued operations, net of tax within the Consolidated Statements of Operations for the year ended December 31, 2013.
	The revenues and results of operations of discontinued operations are summarized as follows (in thousands):
		For the six months ended December 31,
		2013
	Revenues	$	39,868
	Expenses:
	Compensation	$	14,068
	Execution and clearance fees	5,038
	Payments for order flow	9,885
	Other expenses	10,748
	Total Expenses	39,739
	Pre-tax income from discontinued operations	129
	Income tax expense	(49		)
	Income from discontinued operations, net of tax	$	80

Assets_Segregated_or_Held_in_S

Assets Segregated or Held in Separate Accounts Under Federal or Other Regulations	12 Months Ended
	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]	'
Assets Segregated or Held in Separate Accounts Under Federal or Other Regulations	'
	Assets Segregated or Held in Separate Accounts Under Federal or Other Regulations
	Cash and securities segregated under U.S. federal and other regulations primarily relate to the Company’s FCM business and consist of the following (in thousands):
		December 31,
		2013
	Cash and cash equivalents segregated under federal or other regulations	$	183,083
	Receivables from brokers, dealers and clearing organizations (1)	304,294
	Total assets segregated or held in separate accounts under federal or other regulations	$	487,377
	(1) Segregated assets included within Receivables from brokers, dealers and clearing organizations comprise cash and cash equivalents and U.S. government obligations primarily held as deposits with exchange clearing organizations.
	The Company did not have any cash or securities segregated under U.S. Federal and other regulations as of December 31, 2012.

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	The Company’s financial instruments recorded at fair value have been categorized based upon a fair value hierarchy in accordance with accounting guidance, as described in Footnote 3 “Significant Accounting Policies.” The following fair value hierarchy table presents information about the Company’s financial assets and liabilities measured at fair value (in thousands):
		Assets and Liabilities Measured at
		Fair Value on a Recurring Basis
	31-Dec-13	Level 1				Level 2				Level 3				Total
	Assets
	Financial instruments owned, at fair value:
	Equities (1)	$	2,298,785			$	—			$	—			$	2,298,785
	Listed options	339,798				—				—				339,798
	U.S. government and Non-U.S. government obligations	40,053				—				—				40,053
	Corporate debt	43,203				—				—				43,203
	Total Financial instruments owned, at fair value	2,721,839				—				—				2,721,839
	Securities on deposit with clearing organizations (2)	170,235				—				—				170,235
	Investment in CME Group (3)	3,925				—				—				3,925
	Deferred compensation investments (3)	—				117				—				117
	Investment in Deephaven Funds (3)	—				1,958				—				1,958
	Total assets held at fair value	$	2,895,999			$	2,075			$	—			$	2,898,074
	Liabilities
	Financial instruments sold, not yet purchased, at fair value:
	Equities (1)	$	1,851,006			$	—			$	—			$	1,851,006
	Listed options	252,282				—				—				252,282
	U.S. government obligations	15,076				—				—				15,076
	Corporate debt	42,122				—				—				42,122
	Foreign currency forward contracts	—				5,014				—				5,014
	Total liabilities held at fair value	$	2,160,486			$	5,014			$	—			$	2,165,500
	________________________________________
	(1)	Equities of $697.9 million have been netted by their respective long and short positions by CUSIP number.
	(2)	Securities on deposit with clearing organizations consist of U.S. government obligations and are recorded within Receivable from brokers, dealers and clearing organizations on the Consolidated Statements of Financial Condition.
	(3)	Investment in CME Group, Deferred compensation investments and Investment in Deephaven Funds are included within Investments on the Consolidated Statements of Financial Condition.
		Assets and Liabilities Measured at
		Fair Value on a Recurring Basis
	31-Dec-12	Level 1				Level 2				Level 3				Total
	Assets
	Financial instruments owned, at fair value:
	Equities (1)	$	378,933			$	—			$	—			$	378,933
	Listed options	92,305				—				—				92,305
	U.S. government obligations and corporate bonds	68,765				—				—				68,765
	Mutual funds - Bond Funds	114,872				—				—				114,872
	Total Financial instruments owned, at fair value	654,875				—				—				654,875
	Securities on deposit with clearing organizations	7,147				—				—				7,147
	Investment in CME Group	3,040				—				—				3,040
	Investment in Knight preferred shares	199,632				—				—				199,632
	Total assets held at fair value	$	864,694			$	—			$	—			$	864,694
	Liabilities
	Financial instruments sold, not yet purchased, at fair value:
	Equities (1)	$	423,740			$	—			$	—			$	423,740
	Listed options	69,757				—				—				69,757
	U.S. government obligations	19,056				—				—				19,056
	Total Financial instruments sold, not yet purchased, at fair value	512,553				—				—				512,553
	Total liabilities held at fair value	$	512,553			$	—			$	—			$	512,553
	___________________________________
	(1) Equities of $5.9 million have been netted by their respective long and short positions by CUSIP number.
	The Company’s equities, listed options, U.S. government and non-U.S. government obligations, corporate debt and strategic investments that are actively traded are generally classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices or broker or dealer quotations with reasonable levels of price transparency.
	The types of instruments that trade in markets that are not considered to be active, but are valued based on observable inputs such as quoted market prices or alternative pricing sources with reasonable levels of price transparency are generally classified within Level 2 of the fair value hierarchy.
	The Company has no financial instruments classified within Level 3 of the fair value hierarchy.
	The Company’s assets measured at fair value on a nonrecurring basis solely relates to goodwill and intangible assets arising from various acquisitions which would be classified as Level 3 within the fair value hierarchy. See Footnote 11 “Goodwill and Intangible Assets” for additional information.
	There were no transfers of assets or liabilities held at fair value between levels of the fair value hierarchy for any periods presented.
	The Company’s foreign currency forward contracts, deferred compensation investments and its remaining investment in the Deephaven Funds are classified within Level 2 of the fair value hierarchy.
	The following is a description of the valuation basis, techniques and significant inputs used by the Company in valuing its Level 2 assets and liabilities:
	Foreign currency forward contracts
	At December 31, 2013, the Company had foreign currency forward contracts with a notional value of 80.0 million British pounds that are used to hedge the Company’s investment in its European subsidiaries. The fair value of these contracts was determined based upon spot foreign exchange rates, LIBOR interest rates and dealer quotations.
	Deferred compensation investments
	Deferred compensation investments comprise investments in liquid mutual funds that the Company acquires to hedge its obligations to employees and directors under certain non-qualified deferred compensation arrangements. These mutual fund investments can generally be redeemed at any time and are valued based upon quoted market prices.
Investment in Deephaven Funds
Investment in Deephaven Funds represents the Company's residual investment in certain funds that were formerly managed by Deephaven Capital Management, a former Knight subsidiary. These investments are in the process of liquidation and are valued based upon the fair value of the underlying investments within such funds.
Derivative Instruments
Fair value of derivative instruments
The Company enters into derivative transactions, primarily with respect to making markets in listed domestic options. In addition, the Company enters into derivatives to manage foreign currency exposure. Cash flows associated with such derivative activities are included in cash flows from operating activities on the Consolidated Statements of Cash Flows, when applicable.
Futures
During the normal course of business, the Company enters into futures contracts. These financial instruments are subject to varying degrees of risks whereby the fair value of the securities underlying the financial instruments, may be in excess of, or less than, the contract amount. The Company is obligated to post collateral against certain futures contracts.
Futures contracts would be classified as Level 1 if they were required to be reported in the fair value hierarchy; swaps and forward contracts would be classified as Level 2 if they were required to be reported in the fair value hierarchy.
The following tables summarize the fair value of derivative instruments and futures contract trading activities in the Consolidated Statements of Financial Condition and the gains and losses included in the Consolidated Statements of Operations (fair value in thousands):
			31-Dec-13
	Financial Statements		Assets							Liabilities
	Location		Fair Value				Contracts			Fair Value				Contracts
Foreign currency
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		$	89			892			$	142			533
Forward contracts (1)	Financial instruments owned, at fair value		6,913				1			11,515				2
Equity
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		223				1,069			1,089				1,046
Swap contracts	Receivables from/Payables to brokers, dealers and clearing organizations		—				—			18				1
Listed options	Financial instruments owned, at fair value		339,798				730,020			252,282				755,947
Fixed income
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		4,815				18,280			2,259				15,202
Commodity
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		3,392				10,629			1,773				3,806
Total			$	355,230			760,891			$	269,078			776,537
(1) Designated as hedging instrument
			31-Dec-12
	Financial Statements		Assets							Liabilities
	Location		Fair Value				Contracts			Fair Value				Contracts
Foreign currency
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		$	8			500			$	5			110
Forward contracts	Accrued expenses and other liabilities		—				—			110				1
Equity
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		270				766			477				1,070
Swap contracts	Receivables from/Payables to brokers, dealers and clearing organizations		570				1			—				—
Listed options	Financial instruments owned, at fair value		92,305				199,324			69,757				196,804
Fixed income
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		449				49,498			2,014				53,882
Commodity
Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		13				1,060			—				—
Total			$	93,615			251,149			$	72,363			251,867
				Gain (Loss) Recognized
		Financial Statements		For the year
				ended December 31,
		Location		2013				2012				2011
Derivative instruments not designated as hedging instruments:
Foreign currency
Futures contracts		Trading revenues, net		$	12,191			$	19,699			$	25,808
Equity
Futures contracts		Trading revenues, net		50,073				76,089				156,537
Swap contracts		Trading revenues, net		11,736				8,116				18,624
Listed options (1)		Trading revenues, net		37,035				50,446				90,389
Fixed income
Futures contracts		Trading revenues, net		80,511				81,933				170,414
Commodity
Futures contracts		Trading revenues, net		62,215				35,952				24,154
				$	253,761			$	272,235			$	485,926
Derivative instruments designated as hedging instruments:
Foreign exchange - forward contract		Accumulated other comprehensive income		$	(3,298	)		$	—			$	—
(1)	Realized gains and losses on listed equity options relate to the Company’s market making activities in such options. Such market making activities also comprise trading in the underlying equity securities with gains and losses on such securities generally offsetting the gains and losses reported in this table. Gains and losses on such equity securities are also included in Trading revenue, net on the Company’s Consolidated Statements of Operations.
Assets and Liabilities Subject to Netting
The gross amounts of assets and liabilities subject to netting and gross amounts offset in the Consolidated Statements of Financial Condition were as follows (in thousands):
	31-Dec-13	Gross Amounts Recognized				Gross Amounts Offset in the Statements of Financial Condition				Net Amounts of Assets Presented in the Statements of Financial Condition				Gross Amounts Not Offset in the Statement of Financial Condition				Net Amount
														Financial Instruments		Cash Collateral Received
	Assets
	Listed options	$	339,798			$	—			$	339,798			$	—	$	—	$	339,798
	Securities borrowed	1,357,387				—				1,357,387				1,326,220		—		31,167
	Receivable from brokers, dealers and clearing organizations (1)	24,366				—				24,366				24,249		—		117
	Foreign currency forward contracts	6,913				6,501				412				—		—		412
	Futures	8,519				4,369				4,150				—		—		4,150
	Total Assets	$	1,736,983			$	10,870			$	1,726,113			$	1,350,469	$	—	$	375,644
	Liabilities
	Listed options	$	252,282			$	—			$	252,282			$	—	$	10,924	$	241,358
	Securities loaned	733,230				—				733,230				726,948		—		6,282
	Financial instruments sold under agreements to repurchase	640,950				—				640,950				640,948		—		2
	Foreign currency forward contracts	11,515				6,501				5,014				—		—		5,014
	Futures	5,263				5,263				—				—		—		—
	Swaps	18				—				18				—		—		18
	Total Liabilities	$	1,643,258			$	11,764			$	1,631,494			$	1,367,896	$	10,924	$	252,674
(1) Represent reverse repurchase agreements at broker dealer
	31-Dec-12	Gross Amounts Recognized				Gross Amounts Offset in the Statements of Financial Condition				Net Amounts of Assets Presented in the Statements of Financial Condition				Gross Amounts Not Offset in the Statement of Financial Condition				Net Amount
														Financial Instruments		Cash Collateral Received
	Assets
	Listed options	$	92,305			$	—			$	92,305			$	—	$	—	$	92,305
	Securities borrowed	52,261				—				52,261				50,717		—		1,544
	Futures	740				462				278				—		$	—	278
	Total Assets	$	145,306			$	462			$	144,844			$	50,717	$	—	$	94,127
	Liabilities
	Listed options	$	69,757			$	—			$	69,757			$	—	$	1,393	$	68,364
	Futures	2,497				2,497				—				—		—		—
	Total Liabilities	$	72,254			$	2,497			$	69,757			$	—	$	1,393	$	68,364

Collateralized_Transactions

Collateralized Transactions	12 Months Ended
	Dec. 31, 2013
Collateralized Agreements [Abstract]	'
Collateralized Transactions	'
	Collateralized Transactions
	The Company receives financial instruments as collateral in connection with securities borrowed. Such financial instruments generally consist of equity and convertible securities but may include obligations of the U.S. government, federal agencies, foreign government and corporations. In most cases, the Company is permitted to deliver or repledge these financial instruments in connection with securities lending and other secured financings for meeting settlement requirements.
	The table below presents financial instruments at fair value received as collateral and included within Securities borrowed on the Consolidated Statements of Financial Condition that were permitted to be delivered or repledged and that were delivered or repledged by the Company as well as the fair value of financial instruments which could be further repledged by the receiving counterparty (in thousands):
		December 31,		December 31,
		2013		2012
	Collateral permitted to be delivered or repledged	$	1,315,803	$	50,717
	Collateral that was delivered or repledged	1,231,468		50,717
	Collateral permitted to be further repledged by the receiving counterparty	142,938		—
	In order to finance securities positions, the Company also pledges financial instruments that it owns to counterparties who, in turn, are permitted to deliver or repledge them. Under these transactions, the Company pledges certain financial instruments owned to collateralize repurchase agreements and other secured financings. Repurchase agreements and other secured financings are short-term and mature within one year. Financial instruments owned and pledged to counterparties that do not have the right to sell or repledge such financial instruments consist of equity securities.
	The table below presents information about assets pledged by the Company (in thousands):
		December 31,		December 31,
		2013		2012
	Financial instruments owned, at fair value, pledged to counterparties that had the right to deliver or repledge	$	552,242	$	52,261
	Financial instruments owned, at fair value, pledged to counterparties that do not have the right to deliver or repledge	676,956		—

Receivable_from_and_Payable_to

Receivable from and Payable to Brokers, Dealers and Clearing Organizations	12 Months Ended
	Dec. 31, 2013
Brokers and Dealers [Abstract]	'
Receivable from and Payable to Brokers, Dealers and Clearing Organizations	'
	Receivable from and Payable to Brokers, Dealers and Clearing Organizations
	Amounts receivable from and payable to brokers, dealers and clearing organizations consist of the following (in thousands):
		December 31,		31-Dec-12
		2013
	Receivable:
	Clearing organizations and other	$	750,440	$	140,089
	Assets segregated or held in separate accounts under federal or other regulations	304,294		—
	Securities failed to deliver	202,517		2,880
	Total Receivable	$	1,257,251	$	142,969
	Payable:
	Clearing organizations and other	$	425,196	$	15,879
	Securities failed to receive	48,912		8,306
	Total Payable	$	474,108	$	24,185
	Management believes that the carrying value of amounts receivable from and payable to brokers, dealers and clearing organizations approximates fair value since they are short term in nature.

Fixed_Assets_and_Leasehold_Imp

Fixed Assets and Leasehold Improvements	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Fixed Assets and Leasehold Improvements	'
	Fixed Assets and Leasehold Improvements
	Fixed assets and leasehold improvements comprise the following (in thousands):
		Depreciation	December 31,
		Period	2013			2012
	Computer hardware and software	3 years	$	223,141		$	178,187
	Leasehold improvements	*	115,046			60,750
	Telephone systems	5 years	3,848			—
	Furniture and fixtures	7 years	12,227			9,093
			354,262			248,030
	Less - Accumulated depreciation and amortization		(207,594		)	(164,689		)
			$	146,668		$	83,341
	______________________________
	*-Shorter of life of lease or useful life of assets

Investments

Investments	12 Months Ended
	Dec. 31, 2013
Investments [Abstract]	'
Investments	'
	Investments
	Investments comprise strategic investments, including an investment in Knight prior to the Mergers and investment in the Deephaven Funds. Investments consist of the following (in thousands):
		December 31,		December 31,
		2013		2012
	Strategic investments:
	Investments accounted for under the equity method	$	82,234	$	—
	Investments held at fair value	3,925		202,672
	Common stock or equivalent of companies representing less than 20% equity ownership held at adjusted cost	33,813		45,766
	Total Strategic investments	119,972		248,438
	Deferred compensation investments	117		—
	Investment in Deephaven Funds	1,958		—
	Total Investments	$	122,047	$	248,438
	Investments held at fair value, including GETCO's investment in Knight prior to the Mergers, are accounted for as available for sale securities and any unrealized gains or losses are recorded in Other comprehensive income. As a result of the Mergers, the Company recognized a non-cash gain of $128.0 million on its investment in Knight Common Stock, which it recorded within Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013 and reversed any previous unrealized gains out of Other comprehensive income.

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Goodwill and Intangible Assets	'
	Goodwill and Intangible Assets
	Goodwill is assessed for impairment annually or when events indicate that the amounts may be impaired. The Company assesses goodwill for impairment at the reporting unit level. The Company’s reporting units are the components of its business segments for which discrete financial information is available and is regularly reviewed by the Company’s management. As part of the assessment for impairment, the Company considers the cash flows of the respective reporting unit and assesses the fair value of the respective reporting unit as well as the overall market value of the Company compared to its net book value. The assessment of fair value of the reporting units is principally performed using a discounted cash flow methodology with a risk-adjusted weighted average cost of capital which the Company believes to be the most reliable indicator of the fair values of its respective reporting units. The Company also assesses the fair value of each reporting unit based upon its estimated market value and assesses the Company’s overall market value based upon the market price of KCG Class A Common Stock.
	Intangible assets are assessed for recoverability when events or changes in circumstances indicate that the carrying amount of the asset or asset group may not be recoverable. The Company assesses intangible assets for impairment at the “asset group” level which is the lowest level for which identifiable cash flows are largely independent of the cash flows of other groups of assets and liabilities. As part of the assessment for impairment, the Company considers the cash flows of the respective asset group and assesses the fair value of the respective asset group. Step 1 of the impairment assessment for intangibles is performed using undiscounted cash flow models, which indicates whether the future cash flows of the asset group are sufficient to recover the book value of such asset group. When an asset is not considered to be recoverable, step 2 of the impairment assessment is performed using a discounted cash flow methodology with a risk-adjusted weighted average cost of capital to determine the fair value of the intangible asset group. In cases where amortizable intangible assets and goodwill are assessed for impairment at the same time, the amortizable intangibles are assessed for impairment prior to goodwill being assessed.
	As discussed in Footnote 2 "Merger of GETCO and Knight", as a result of the Mergers, $155.4 million and $11.6 million in identifiable intangible assets and goodwill, respectively, were recorded by the Company on the date of the Mergers.
	No events occurred in 2013 or 2012 that would indicate that the carrying amounts of the Company’s goodwill or intangible assets may not be recoverable. In December 2013, the Company assessed the impairment of goodwill and intangible assets as part of its annual assessment and concluded that there was no impairment.
	The following table summarizes the Company’s Goodwill by segment (in thousands):
		December 31,				31-Dec-12
		2013
	Market Making	$	15,427			$	4,645
	Global Execution Services	832				—
	Total	$	16,259			$	4,645
	Intangible assets with definite useful lives are amortized over their estimated remaining useful lives, the majority of which have been determined to range from three to 12 years. The weighted average remaining life of the Company’s intangible assets with definite useful lives at December 31, 2013 and December 31, 2012 is approximately six years and nine years, respectively.
	The following tables summarize the Company’s Intangible assets, net of accumulated amortization by segment and type (in thousands):
		December 31,				31-Dec-12
		2013
	Market Making
	Trading rights	$	48,920			$	48,903
	Technology	53,315				3,487
	Total	102,235				52,390
	Global Execution Services
	Customer relationships	33,278				—
	Trade names	3,800				—
	Technology	38,682				—
	Total	75,760				—
	Corporate and Other
	Technology	13,500				—
	Consolidated Total	$	191,495			$	52,390
			December 31,				31-Dec-12
			2013
	Customer relationships (1)	Gross carrying amount	$	35,000			$	—
		Accumulated amortization	(1,722		)		—
		Net carrying amount	33,278				—
	Trading rights (2)	Gross carrying amount	62,450				58,095
		Accumulated amortization	(13,530		)		(9,192		)
		Net carrying amount	48,920				48,903
	Trade names (3)	Gross carrying amount	4,000				—
		Accumulated amortization	(200		)		—
		Net carrying amount	3,800				—
	Technology (4)	Gross carrying amount	120,346				5,580
		Accumulated amortization	(14,849		)		(2,093		)
		Net carrying amount	105,497				3,487
	Total	Gross carrying amount	221,796				63,675
		Accumulated amortization	(30,301		)		(11,285		)
		Net carrying amount	$	191,495			$	52,390
	________________________________________
	(1)	Customer relationships relate to KCG Hotspot and KCG BondPoint. The weighted average remaining life is approximately 10 years as of December 31, 2013. Lives may be reduced depending upon actual retention rates.
	(2)	Trading rights provide the Company with the rights to trade on certain exchanges. The weighted average remaining life of trading rights with definite useful lives is approximately eight and nine years as of December 31, 2013 and December 31, 2012, respectively. As of December 31, 2013 and 2012, $7.6 million and $6.3 million, respectively, of trading rights have indefinite useful lives.
	(3)	Trade names relate to KCG Hotspot and KCG BondPoint. The weighted average remaining life is approximately ten years as of December 31, 2013.
	(4)	The weighted average remaining life for technology, including capitalized software, is approximately four and three years as of December 31, 2013 and December 31, 2012, respectively.
	The following table summarizes the Company’s amortization expense from continuing operations relating to Intangible assets (in thousands):
		For the year ended December 31,
		2013				2012				2011
	Amortization expense	$	19,211			$	5,518			$	3,595
	As of December 31, 2013, the following table summarizes the Company’s estimated amortization expense for future periods (in thousands):
		Amortization
		expense
	For the year ended December 31, 2014	$	33,542
	For the year ended December 31, 2015	32,617
	For the year ended December 31, 2016	31,527
	For the year ended December 31, 2017	30,396
	For the year ended December 31, 2018	19,396

Debt

Debt	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	The carrying value and fair value of the Company's debt is as follows (in thousands):
		31-Dec-13				31-Dec-12
		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	Notes	$	—	$	—	$	15,000	$	15,000
	Cash Convertible Senior Subordinated Notes	117,259		118,432		—		—
	Senior Secured Notes	305,000		320,823		—		—
	First Lien Credit Facility	235,000		235,000		—		—
	Total Debt	$	657,259	$	674,255	$	15,000	$	15,000
	The fair value of the Cash Convertible Senior Subordinated Notes and Senior Secured Notes is based upon the value of such debt in the secondary market. The carrying value of the First Lien Credit facility approximated fair value as it was not materially sensitive to shifts in interest rates due to its floating interest rate, which also considers changes in the Company's credit risks and financial condition. These liabilities would all be categorized as Level 2 in the fair value hierarchy if they were required to be recorded at fair value.
	Notes
	In October 2011, the Company issued $15.0 million in notes to a single lender. The notes bore interest at 5.95% per annum, required no principal amortization over the term and were scheduled to mature in October 2018. The note agreement included certain covenants which required the Company, among other things, to maintain compliance with debt to net worth ratios, maintain minimum levels of liquid net assets and maintain minimum net capital levels in regulated subsidiaries. At December 31, 2012, the Company was in compliance with these covenants. In anticipation of the Mergers, on May 31, 2013, the Company provided irrevocable notice to the lender to prepay the notes. The $15.0 million in notes were subsequently repaid on July 1, 2013 along with accrued interest and a $3.0 million early termination payment.
	Cash Convertible Senior Subordinated Notes
	In March 2010, Knight issued $375.0 million aggregate principal amount of Cash Convertible Senior Subordinated Notes (the “Convertible Notes”) due on March 15, 2015 in a private offering exempt from registration under the Securities Act of 1933, as amended.
	The Convertible Notes bear interest at a rate of 3.50% per year, payable semi-annually in arrears, on March 15 and September 15 of each year, commencing on September 15, 2010 and will mature on March 15, 2015, subject to earlier repurchase or conversion. The Convertible Notes are reported as Debt in the Company’s Consolidated Statements of Financial Condition.
	As a result of the Mergers, on July 1, 2013, KCG became a party to Knight's $375.0 million Convertible Notes. On July 1, 2013, the Company delivered a notice (the “Convertible Notes Notice”) to the holders of the Notes. The Convertible Notes Notice advised holders of the Convertible Notes of the following (among others):
	•	The completion of the Mergers on July 1, 2013 and the results of the election of the holders of KCG Class A Common Stock to receive cash consideration for such KCG Class A Common Stock constitutes a “Fundamental Change";
	•	Each holder of the Convertible Notes has the right to deliver a “Fundamental Change Repurchase Notice ” requiring the Company to repurchase all or any portion of the principal amount of the Convertible Notes at a Fundamental Change Repurchase Price of 100% of the principal amount plus accrued and unpaid interest on August 5, 2013, the Fundamental Change Repurchase Date; and
	•	The Company deposited with the paying agent an amount of money sufficient to repurchase all of the Convertible Notes to be repurchased; and upon payment by the paying agent such Convertible Notes will cease to be outstanding.
	On July 1, 2013, $375.0 million, which was the amount needed to repurchase the aggregate amount of Knight's Convertible Notes in full at maturity, was deposited in a cash collateral account under the sole dominion and control of the collateral agent under the First Lien Credit Facility (the "Collateral Account").
	After the Mergers, a total of $257.7 million in principal amount of the Convertible Notes were repurchased using funds deposited in the Collateral Account. The repurchase included accrued and unpaid interest of $3.6 million. In October 2013, the funds remaining in the Collateral Account were used to repay a portion of the First Lien Credit Facility. As of December 31, 2013, there were no funds in the Collateral Account.
	Debt incurred in connection with Mergers
	In connection with the Mergers, KCG entered into a series of debt agreement transactions. Described below are the details of these transactions.
	Senior Secured Notes
	On June 5, 2013 GETCO Financing Escrow LLC (“Finance LLC”), a wholly-owned subsidiary of GETCO, issued 8.250% senior secured notes due 2018 in the aggregate principal amount of $305.0 million (the “Senior Secured Notes”) pursuant to an indenture, dated June 5, 2013 (as amended, the "Senior Secured Notes Indenture"). On July 1, 2013, KCG entered into a first supplemental indenture (the “First Supplemental Indenture”) pursuant to which KCG assumed all of the obligations of Finance LLC which comprised the Senior Secured Notes plus certain escrow agent fees and expenses of $3.0 million.
	On July 1, 2013, KCG and certain subsidiary guarantors (the "Guarantors") under the First Lien Credit Facility, as defined below, entered into a Second Supplemental Indenture, whereby the Senior Secured Notes and the obligations under the Senior Secured Notes Indenture will be fully and unconditionally guaranteed on a joint and several basis by the Guarantors and are secured by second-priority pledges and second-priority security interests in, and mortgages on, the collateral securing the First Lien Credit Facility, subject to certain exceptions.
	The Senior Secured Notes mature on June 15, 2018 and bear interest at a rate of 8.250% per year, payable on June 15 and December 15 of each year, beginning on December 15, 2013.
	The Senior Secured Notes Indenture contains customary affirmative and negative covenants, including limitations on indebtedness, liens, hedging agreements, investments, loans and advances, asset sales, mergers and acquisitions, dividends, transactions with affiliates, prepayments of other indebtedness, restrictions on subsidiaries and issuance of capital stock. As of December 31, 2013, the Company was in compliance with the covenants.
	On July 1, 2013, KCG and the Guarantors entered into a joinder to the registration rights agreement dated June 5, 2013, (the "Senior Secured Notes Registration Rights Agreement") between Finance LLC and Jefferies LLC as representative of the initial purchasers of the Senior Secured Notes. Pursuant to the registration rights agreement, KCG shall use commercially reasonable efforts to (i) file an exchange offer registration statement with the SEC with respect to a registered offer to exchange the Senior Secured Notes, (ii) issue exchange securities within 365 days after June 5, 2013, and, (iii) in certain circumstances, file a shelf registration statement with respect to resales of the Senior Secured Notes. If KCG and the Guarantors fail to comply with certain obligations under the Senior Secured Notes Registration Rights Agreement, additional interest of up to 1.00% per annum will accrue on the Senior Secured Notes.
	In October 2013, the Company received consents from 99.7% of its registered holders ("Holders") of the Senior Secured Notes to amend, among other things, the terms of the Senior Secured Notes among the Company, The Bank of New York Mellon, as trustee and collateral agent (the “Trustee”), and the guarantors.
	As a result, the Company entered into the Third Supplemental Indenture with the Trustee to amend the Senior Secured Notes Indenture to permit the purchase, redemption or repayment of the Credit Agreement at any price, including at a premium or at a discount from the face value thereof, with any available cash.
	First Lien Credit Facility
	On July 1, 2013, KCG, as borrower, entered into a first lien senior secured credit agreement (the “Credit Agreement”) with Jefferies Finance LLC and Goldman Sachs Bank USA. The Credit Agreement was in the amount of $535.0 million (the “First Lien Credit Facility”), all of which was drawn on July 1, 2013. The First Lien Credit Facility also provides for a future uncommitted incremental first lien senior secured revolving credit facility of up to $50.0 million, including letter of credit and swingline sub-facilities, on certain terms and conditions contained in the Credit Agreement. For the six months ended December 31, 2013, there were no borrowings made against the $50.0 million first lien senior secured revolving credit facility.
	The First Lien Credit Facility bears interest, at KCG's option, at a rate based on the prime rate (“First Lien Prime Rate Loans”) or based on LIBOR (“First Lien Eurodollar Loans”). First Lien Prime Rate Loans bear interest at a rate per annum equal to the greatest of prime rate, 2.25%, the federal funds rate plus 0.50%, and an adjusted one-month LIBOR rate plus 1.00%, in each case plus an applicable margin of 3.50%. First Lien Eurodollar Loans bear interest at a rate per annum equal to the adjusted LIBOR rate (subject to a 1.25% LIBOR floor) corresponding to the interest period plus an applicable margin of 4.50% per annum. As of December 31, 2013, the interest rate was 5.75% per annum.
	The First Lien Credit Facility matures on December 5, 2017. The First Lien Credit Facility requires an amortization payment of $235.0 million on July 1, 2014 followed by quarterly amortization payments of $7.5 million on each September 30, December 31, March 31 and June 30, with the balance due on maturity.
	Optional prepayments of borrowings under the First Lien Credit Facility are permitted at any time, without premium or penalty, subject, however, to a 1% prepayment premium for optional prepayments of the First Lien Credit Facility made prior to July 1, 2014 with a new or replacement term loan facility with an “effective” interest rate less than that applicable to the First Lien Credit Facility.
	The First Lien Credit Facility is fully and unconditionally guaranteed on a joint and several basis by all of KCG's existing and future direct and indirect 100% owned domestic subsidiaries, other than certain subsidiaries including regulated broker dealers and other regulated subsidiaries that, in each case, are not permitted to provide such guarantees under applicable law.
	The First Lien Credit Facility contains customary affirmative and negative covenants, including limitations on indebtedness, liens, hedging agreements, investments, loans and advances, asset sales, mergers and acquisitions, dividends, transactions with affiliates, prepayments of other indebtedness, restrictions on subsidiaries, capital expenditures and issuance of capital stock. It also contains financial maintenance covenants establishing a maximum consolidated first lien leverage ratio, a minimum consolidated interest coverage ratio and a minimum consolidated tangible net worth.
	In connection with the consent solicitation and the Third Supplemental Indenture, the Company entered into an Amendment to its Credit Agreement with the consent of the requisite percentage of lenders under its First Lien Credit Facility. The Credit Agreement Amendment permits the Company to prepay a portion of the principal amount of borrowings under the First Lien Credit Facility from time to time for a period of 60 days following the effective date of the Credit Agreement Amendment out of the cash set aside in the Collateral Account under the sole dominion and control of the collateral agent under the First Lien Credit Facility for repayments of the Convertible Notes, after which period the remaining cash in the Collateral Account will be required to be used to prepay a portion of the principal amount of borrowings under the First Lien Credit Facility. On October 23, 2013, as permitted by the Credit Agreement Amendment, the Company applied 100% of the $117.3 million cash set aside in the Collateral Account to prepay a portion of the principal amount of borrowings under the First Lien Credit Facility. The Credit Agreement Amendment also permits the purchase, redemption or repayment of the Convertible Notes at any price, including at a premium or at a discount from the face value thereof, with any available cash.
	The Company incurred issuance costs of $37.4 million in connection with the issuance of Senior Secured Notes, Credit Agreement and consent solicitation. The remaining issuance costs are recorded within Other assets on the Consolidated Statements of Financial Condition and are amortized over the respective terms of the Senior Secured Notes and the Credit Agreement. Including issuance costs, the Senior Secured Notes and Credit Agreements have effective yields of 9.0% and 8.3%, respectively.
	During the fourth quarter of 2013, the Company repaid $300.0 million of principal of the First Lien Credit Facility. A portion of the $300.0 million was drawn from $117.3 million in cash held in the Collateral Account and the remainder of the $300.0 million was paid out of available cash including proceeds from the sale of Urban. In conjunction with these payments, the Company wrote down $13.2 million of its capitalized debt costs associated with the Credit Agreement.
	Subsequent to December 31, 2013, the Company made a further $100.0 million principal prepayment under the Credit Agreement. See Footnote 26 "Subsequent Events" for further discussion.
	Revolving Credit Agreement
	On July 1, 2013, OCTEG, LLC (“OCTEG”), and Knight Capital Americas LLC ("KCA") now named KCG Americas LLC, each of which are wholly-owned broker dealer subsidiaries of KCG effective July 1, 2013, as borrowers, and KCG, as guarantor, entered into a credit agreement (the “OCTEG-KCA Facility Agreement”) with a consortium of banks and financial institutions. The OCTEG-KCA Facility Agreement replaces an existing credit agreement, dated as of June 6, 2012, among OCTEG and three banks.
	The OCTEG-KCA Facility Agreement comprises two classes of revolving loans in a total committed amount of $450.0 million, together with a swingline facility with a $50.0 million sub-limit, subject to two borrowing bases (collectively, the “OCTEG-KCA Revolving Facility”): Borrowing Base A and Borrowing Base B. The OCTEG-KCA Revolving Facility also provides for a future increase of the revolving credit facility of up to $300.0 million to a total of $750.0 million on certain terms and conditions.
	Borrowings under the OCTEG-KCA Facility shall bear interest, at the applicable borrower's option, at a rate based on the federal funds rate (“Base Rate Loans”) or based on LIBOR (“Eurodollar Loans”), in each case plus an applicable margin. For each Base Rate Loan, the interest rate per annum is equal to the greater of the federal funds rate or an adjusted one-month LIBOR rate plus (a) for each Borrowing Base A loan, a margin of 1.75% per annum and (b) for each Borrowing Base B loan, a margin of 2.25% per annum. For each Eurodollar Loan, the interest rate per annum is equal to an adjusted LIBOR rate corresponding to the interest period plus (a) for each Borrowing Base A loan, a margin of 1.75% per annum and (b) for each Borrowing Base B loan, a margin of 2.25% per annum. As of December 31, 2013, there were no outstanding borrowings under the OCTEG-KCA Facility Agreement.
	The proceeds of the Borrowing Base A loans are available to both OCTEG and KCA and may be used solely to finance the purchase and settlement of securities. The proceeds of Borrowing Base B loans are available solely to KCA and may be used solely to fund clearing deposits with the National Securities Clearing Corporation.
	The borrowers are being charged a commitment fee at a rate of 0.35% per annum on the average daily amount of the unused portion of the OCTEG-KCA Facility Agreement.
	The loans under the OCTEG-KCA Facility Agreement will mature on June 6, 2015. The OCTEG-KCA Revolving Facility is fully and unconditionally guaranteed on an unsecured basis by KCG and, to the extent elected by OCTEG or KCA, any of their respective subsidiaries. It is secured by first-priority pledges of and liens on certain eligible securities, subject to applicable concentration limits, in the case of Borrowing Base A loans, and by first-priority pledges of and liens on the right to the return of certain eligible NSCC margin deposits, in the case of Borrowing Base B loans.
	The OCTEG-KCA Revolving Facility includes customary affirmative and negative covenants, including limitations on indebtedness, liens, hedging agreements, investments, loans and advances, asset sales, mergers and acquisitions, dividends, transactions with affiliates, restrictions on subsidiaries, issuance of capital stock, negative pledges and business activities. It contains financial maintenance covenants establishing a minimum total regulatory capital for each of OCTEG and KCA, a maximum total asset to total regulatory capital ratio for each of OCTEG and KCA, a minimum excess net capital limit for each of OCTEG and KCA, a minimum liquidity ratio for KCA, and a minimum tangible net worth threshold for KCG. As of December 31, 2013, the Company was in compliance with the covenants.
	In connection with the OCTEG-KCA Revolving Facility, the Company incurred issuance costs of $1.2 million which is recorded within Other assets on the Consolidated Statements of Financial Condition and is being amortized over the term of the facility.
	OCTEG and KCA shall each be obligated only with respect to the principal and interest of their own borrowings, and not the interest and principal of the other borrower's borrowings.
	The OCTEG-KCA Revolving Facility was amended on October 24, 2013 to permit OCTEG to be removed as a borrower under the OCTEG-KCA Revolving Facility. As of January 1, 2014, OCTEG was merged with and into KCA and KCA was renamed KCG Americas LLC.
	The Company recorded expenses with respect to the Debt as follows (in thousands):
		For the year ended December 31,
		2013		2012		2011
	Interest expense	$	34,138	$	1,194	$	164
	Amortization of debt issuance cost (1)	16,832		276		—
	Commitment fee (1)	792		1,034		—
	Total	$	51,762	$	2,504	$	164
	(1)	$3.6 million is included in Other expense

Related_Parties

Related Parties	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Related Parties	'
	Related Parties
	The Company interacts with two related parties as part of its normal day-to-day operations. It earns revenues, incurs expenses and maintains balances with these related parties or their affiliates. As of the date and period indicated below, the Company had the following balances and transactions with the related parties or their affiliates as follows (in thousands):
	Statement of Operations	For the year ended
		December 31,
		2013
	Revenues
	Commissions and fees	$	2,583
	Trading revenues, net	437
	Interest, net	71
	Total revenues from related parties	$	3,091
	Expenses
	Execution and clearance fees	$	(5,706	)
	Interest expense	102
	Other expense	146
	Total expenses incurred with respect to related parties	$	(5,458	)
	Statement of Financial Condition	December 31,
		2013
	Assets
	Securities borrowed	$	57,732
	Receivable from brokers, dealers and clearing organizations	20,826
	Other assets	277
	Liabilities
	Securities loaned	$	116,062
	Payable to brokers, dealers and clearing organizations	17,820
	Accrued expenses and other liabilities	179
	In the ordinary course of business, the Company enters into foreign exchange contracts with related parties.
	During 2013, the Company paid one of the related parties $49.8 million in fees related to financing and advisory activities.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2013
Share-based Compensation [Abstract]	'
Stock-Based Compensation	'
	Stock-Based Compensation
	KCG Equity Incentive Plan
	The Knight Capital Group, Inc. Amended and Restated 2010 Equity Incentive Plan was established to provide long-term incentive compensation to employees and directors of the Company. As a result of the Mergers, on July 1, 2013, this plan was assumed by KCG and was renamed the KCG Holdings, Inc. Amended and Restated Equity Incentive Plan ("the KCG Plan"). At such time, the Knight Capital Group, Inc. 2009 Executive Incentive Plan was also assumed by KCG in connection with the Mergers and was renamed the KCG Holdings, Inc. Amended and Restated Executive Incentive Plan. As of the closing of the Mergers, the number of shares reserved for issuance under the KCG Plan was 20.7 million (based on a conversion ratio of one third of a share of KCG Class A Common Stock for each share of Knight Class A Common Stock). At a special meeting of the Company's stockholders on December 19, 2013, the Company's stockholders approved an increase to the number of shares authorized for grant under the KCG Plan from 20.7 million shares to 32.7 million shares (subject to adjustment as provided for under the KCG Plan).
	The KCG Plan is administered by the Compensation Committee of the Company’s Board of Directors, and allows for the grant of options, SARs, restricted stock and RSUs (collectively, the “awards”), as defined by the KCG Plan. In addition to overall limitations on the aggregate number of awards that may be granted, the KCG Plan also limits the number of awards that may be granted to a single individual. The KCG Plan replaced prior Knight stockholder-approved equity plans for future equity grants and no additional grants will be made under those historical Knight stock plans. However, the terms and conditions of any outstanding equity grants under the historical Knight stock plans are not affected.
	As a result of the Mergers on July 1, 2013, each outstanding Knight stock option, whether vested or unvested, was automatically replaced with an option to purchase KCG Class A Common Stock equal to one third of the number of shares of Knight Common Stock subject to such original stock option immediately prior to the completion of the Mergers (rounded down to the nearest whole share of KCG Class A Common Stock). The exercise price per share of KCG Class A Common Stock is equal to the exercise price per share of Knight Common Stock subject to such Company stock option multiplied by three (rounded up to the nearest whole cent). Pursuant to the terms of the applicable Knight stock plans and award agreements, each option granted on or prior to December 19, 2012 immediately vested. There were no Knight stock options granted subsequent to December 19, 2012 through June 30, 2013.
	As a result of the Mergers, each Knight restricted share granted after December 19, 2012 and each outstanding Knight RSU was replaced with a KCG restricted share or RSU, as applicable, in respect of one third of a share of common stock of KCG (rounded to the nearest whole share). Knight restricted share and RSU awards granted on or prior to December 19, 2012 (except for RSUs subject to performance-based vesting conditions) automatically vested upon the completion of the Mergers. Knight awards granted after December 19, 2012 (and RSUs granted on or prior to December 19, 2012 that were subject to performance-based vesting conditions) will continue to vest in accordance with their existing vesting schedule, subject to acceleration under certain circumstances.
	Restricted Shares and Restricted Stock Units
	Eligible employees and directors may receive restricted shares and/or RSUs (collectively “restricted awards”) as a portion of their total compensation. The majority of restricted awards vest ratably over three years and are subject to accelerated vesting, or continued vesting, following certain termination circumstances, in accordance with the applicable award documents. For certain restricted awards, the Company has the right to fully vest employees and directors upon retirement and in certain other circumstances.
	The Company measures compensation cost related to restricted awards based on the fair value of KCG Class A Common Stock at the date of grant. Compensation expense from continuing operations relating to restricted awards, which is primarily recorded in Employee compensation and benefits, and the corresponding income tax benefit, which is recorded in Income tax (benefit) expense on the Consolidated Statements of Operations are presented in the following table (in thousands):
			For the year ended December 31,
			2013
	Stock award compensation expense		$	33,067
	Income tax benefit		11,573
	The following table summarizes restricted awards activity for the six months ended December 31, 2013 (awards in thousands):
			Restricted Stock Units
			Number of			Weighted-
			Units			Average
						Grant date
						Fair Value
	1-Jul-13
	Conversion of outstanding Knight RSUs		3,251			$	11.22
	Granted		6,050			10.57
	Vested		(391	)		11.89
	Forfeited		(490	)		11.4
	Outstanding at December 31, 2013		8,420			$	10.71
	There is $67.3 million of unamortized compensation related to the unvested restricted awards outstanding at December 31, 2013. The cost of these unvested restricted shares is expected to be recognized over a weighted average life of 2.2 years.
	Stock Options and Stock Appreciation Rights
	The Company’s policy is to grant options for the purchase of shares of KCG Class A Common Stock and SARs to purchase or receive the cash value of shares of KCG Class A Common Stock, in each case with an exercise price not less than the market value of KCG Class A Common Stock on the grant date. Options and SARs generally vest ratably over a three year period and expire on the fifth or tenth anniversary of the grant date, pursuant to the terms of the applicable award agreement. Options and SARs continue to vest following certain termination circumstances, in accordance with the applicable award agreements. Options and SARs are otherwise canceled if employment is terminated before the end of the relevant vesting period. The Company’s policy is to issue new shares upon option exercises by its employees and directors. The Company may issue new shares or provide a cash payment upon SARs exercises by its employees.
	The fair value of each option and SAR granted is estimated as of its respective grant date using the Black-Scholes option-pricing model. Stock options and SARs are granted with exercise prices equal to or greater than the market value of the Company’s common stock at the date of grant as defined by the stock plans. The principal assumptions utilized in valuing options and SARs and the methodology for estimating such model inputs include: 1) risk-free interest rate—estimate is based on the yield of U.S. zero coupon securities with a maturity equal to the expected life of the option or SAR; 2) expected volatility—estimate is based on several factors including implied volatility of market-traded options on the Company’s common stock on the grant date and the volatility of the Company’s common stock; and 3) expected option or SAR life—estimate is based on internal studies of historical experience and projected exercise behavior based on different employee groups and specific option and SAR characteristics, including the effect of employee terminations. Based on the results of the model, the weighted-average fair value of the stock options granted in 2013 was $3.15 per option. There were no stock options granted in 2012 or 2011.
	The weighted average assumptions used for stock options granted were as follows:
			2013
	Dividend yield		—	%
	Expected volatility		35	%
	Risk-free interest rate		1	%
	Expected life (in years)		3.5
	Compensation expense from continuing operations relating to stock options and SARs, all of which was recorded in Employee compensation and benefits, as well as the corresponding income tax benefit, which is recorded in Income tax benefit on the Consolidated Statements of Operations are as follows (in thousands):
			For the year ended December 31,
			2013
	Stock option and SAR compensation expense		$	1,813
	Income tax benefit		635
	The following table summarizes stock option and SAR activity and stock options exercisable for the six months ended December 31, 2013 (awards in thousands):
		Number of Stock Awards			Weighted-				Aggregate				Weighted-
					Average				Intrinsic				Average
					Exercise				Value				Remaining
					Price								Life (years)
	1-Jul-13	—			$	—
	Conversion of outstanding Knight options	782			41.25
	Granted at market value (1)	4,323			15.19
	Exercised	—			—
	Forfeited or expired	(138	)		45.32
	Outstanding at December 31, 2013 (1)	4,967			$	18.45			$	3,621			4.23
	Exercisable at December 31, 2013	644			$	40.37			$	—			2.23
	Available for future grants at December 31, 2013 *	19,160
	* Represents both options and awards available for grant.
	(1) Includes 1.7 million of SARs.
			Options Outstanding									Options Exercisable
	Range of Exercise Prices		Outstanding			Weighted-		Weighted-				Number		Weighted-
			at 12/31/13			Average		Average				Exercisable		Average
						Remaining		Exercise				at 12/31/13		Exercise
						Contractual		Price						Price
						Life
	$8.24 - $8.24		833			4.61		$	8.24			—		$	—
	$8.25- $8.25		91			4.64		8.25				—		—
$11.65 - $11.65		1,700			4.51		11.65				—		—
$22.50 - $22.50		1,700			4.51		22.5				—		—
$23.70 - $53.91		640			2.23		40.28				640		40.28
$58.08 - $58.08		3			3.01		58.08				3		58.08
		4,967			4.23		$	18.45			643		$	40.37
The aggregate intrinsic value is the amount by which the closing price of the Company’s common stock exceeds the exercise price of the stock options multiplied by the number of shares. There were no stock options exercised during the year ended December 31, 2013.
There is $7.0 million unamortized compensation related to unvested stock options and SARs outstanding at December 31, 2013. The cost of these unvested awards is expected to be recognized over a weighted average life of 1.9 years.
Incentive units
Prior to the Mergers, GETCO awarded deferred compensation to its employees in the form of incentive units that generally vest over time. The value of these incentive units was determined based on the same methodology used to value the GETCO Class B unit awards and the amount expensed was determined based on this valuation multiplied by the percent vested. In connection with the Mergers, all outstanding unvested incentive units vested and were converted into units based on the applicable exchange ratio of GETCO units to KCG Class A Common Stock. The units are marked to the current stock price of KCG Class A Common Stock at the end of each period with the resulting change in the liability reflected as either an expense or gain included in Employee compensation and benefits. Given that the units vested in connection with the Mergers, the Company fully amortized the units as of June 30, 2013. The accelerated amortization of incentive units recorded during the year ended December 31, 2013 was $1.3 million. Deferred compensation payable at December 31, 2013 and December 31, 2012 related to incentive units was $3.8 million and $3.5 million, respectively, and is included in Accrued compensation expense on the Consolidated Statements of Financial Condition.
The following is a summary of the changes in the incentive units for the year ended December 31, 2013 (units in thousands):
		Vested			Unvested
Incentive units at January 1, 2013		24			45
Issued		1			12
Vested		53			(53	)
Exercised		(28	)		—
Canceled		(1	)		(4	)
Incentive units at December 31, 2013		49			—
Class B units
Prior to the Mergers, GETCO granted membership unit awards to employees in the form of Class B units. The Class B units were valued at the date of grant based on the estimated enterprise value of GETCO. Prior to 2012, these non-voting units vested in full three years from the grant date, provided certain conditions of employment and performance were met by the employee. In 2012, GETCO changed the vesting of units granted in 2012 to annual vesting of one-third of the units over a three year period. Upon termination of employment, GETCO had the option to repurchase all or a portion of the units granted within six months. The purchase price for the unvested units was determined as a percentage of grant date fair value. GETCO classified these unit awards as equity as the employees received full membership rights with respect to allocation of income and participation in member distributions. In connection with the Mergers, all outstanding unvested Class B units vested on June 25, 2013. The accelerated amortization of Class B units recorded during the year ended December 31, 2013 was $9.4 million.
The following is a schedule of the changes in GETCO's unvested Class B units (units in thousands):
		Units			Weighted Average Grant Price
Unvested as of January 1, 2013		417			$	89.99
Issued		58			73.54
Vested		(438	)		87.86
Forfeited		(37	)		89.28
Unvested as of December 31, 2013		—
Class E units
In 2012, GETCO also granted employees profit interests in the form of Class E units. Prior to 2012, Class E units primarily vested in full three years from the grant date. For units granted in 2012, GETCO changed the vesting of Class E units to an annual vesting of one-third of the units over the three year period and provided GETCO an option to repurchase the units at the end of 5 years. Class E units allowed for future appreciation in excess of the GETCO's value over a certain strike price per unit and allocation of income once the units are vested. Upon the departure of an employee, the Class E units were forfeited whether vested or not, and if vested, the cash value of the Class E units above their strike price was paid to the employee. GETCO classified these unit awards as equity. In connection with the Mergers all outstanding unvested Class E units vested on June 25, 2013 and were canceled for no consideration. The accelerated amortization of the Class E units recorded during the year ended December 31, 2013 was $3.5 million, respectively.
The following is a schedule of the changes in GETCO's unvested Class E units (units in thousands):
		Units			Weighted Average Grant Price
Unvested as of December 31, 2012		476			$	36.78
Issued		—			—
Vested		(442	)		37.24
Forfeited		(34	)		30.89
Unvested as of December 31, 2013		—
Compensation expense (benefit) related to the Class B, Class E and Incentive units, all of which are recorded within Employee compensation and benefits on the Consolidated Statements of Operations are as follows (in thousands):
		For the year ended December 31,
		2013				2012				2011
Class B and E units		$	19,860			$	12,320			$	40,466
Incentive units		2,446				1,264				858
Total		$	22,306			$	13,584			$	41,324

Employee_Benefit_Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]	'
Employee Benefit Plan	'
	Employee Benefit Plan
	The Company sponsors a 401(k) profit sharing plan (the “401(k) Plan”) in which most of its employees are eligible to participate. Under the terms of the 401(k) Plan, the Company is required to make annual contributions to the 401(k) Plan equal to 100% of the contributions made by its employees, up to annual limits, however for 2013, such provisions only applied to Knight employees. The total expense recognized with respect to the 401(k) Plan is included in Employee compensation and benefits on the Consolidated Statements of Operations, as follows (in thousands):
	For the year ended December 31, 2013	$	2,959

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	Upon completion of the Mergers, the Company became subject to U.S. corporate income taxes and the Company and its subsidiaries will file a consolidated federal income tax return as well as combined state income tax returns in certain jurisdictions. In other jurisdictions, the Company and its subsidiaries will file separate company state and local income tax returns.
	Prior to the Mergers, GETCO and the majority of its subsidiaries were treated as partnerships or disregarded entities for U.S. income tax purposes and, accordingly, were not subject to federal income taxes. Instead, former GETCO members were liable for federal income taxes on their proportionate share of taxable income; however, certain subsidiaries were subject to corporate income taxes related to the taxable income generated by their operations.
	As described in Footnote 2 “Merger of GETCO and Knight”, following the Mergers the Company recorded $62.3 million of deferred tax assets as a result of recording Knight’s assets and liabilities under the purchase method of accounting as well as recording the value of Knight’s NOLs and tax credit carryforwards as described below.
	As a result of the Company becoming subject to U.S. corporate income taxes, the Company also recorded a nonrecurring $103.5 million deferred tax benefit and corresponding deferred tax asset relating to GETCO's existing tax attributes. This deferred tax asset primarily relates to differences between GETCO’s book and tax bases in its intangible assets and its strategic investments.
	The (benefit) provision for income taxes from continuing operations consists of (in thousands):
		For the years ended December 31,
		2013			2012			2011
	Current:
	U.S. federal	$	(194	)	$	(627	)	$	2,047
	U.S. state and local	2,902			618			1,218
	Non U.S.	3,773			8,708			29,910
		$	6,481		$	8,699		$	33,175
	Deferred:
	U.S. federal	$	(108,077	)	1,771			(949		)
	U.S. state and local	—			1,046			(263		)
	Non U.S.	(599		)	(1,240		)	(1,122		)
		$	(108,676	)	$	1,577		$	(2,334	)
	Provision (benefit) for income taxes	$	(102,195	)	$	10,276		$	30,841
	The following table reconciles the U.S. federal statutory income tax to the Company's actual income tax from continuing operations (in thousands):
		For the years ended December 31,
		2013			2012			2011
	U.S. federal statutory income tax (benefit) expense	$	6,235		$	9,249		$	67,739
	Income not subject to U.S. corporate income tax	(14,071		)	(7,095		)	(65,718		)
	U.S. state and local income taxes, net of U.S. federal income tax effect	1,886			772			478
	Deferred tax benefit resulting from the Company becoming subject to U.S. corporate income taxes	(103,499		)	—			—
	Nondeductible expenses (1)	3,627			200			133
	Foreign taxes	3,603			7,468			29,118
	Other, net	24			(318		)	(909		)
	Income tax (benefit) expense	$	(102,195	)	$	10,276		$	30,841
	(1) Nondeductible expenses include nondeductible compensation and meals and entertainment.
	Deferred income taxes reflect the net tax effects of temporary differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when such differences are expected to reverse. Valuation allowances recorded on the balance sheet dates are necessary in cases where management believes that it is more likely than not that some portion or all of the deferred tax assets will not be realized.
		For the years ended December 31,
		2013			2012
	Deferred tax assets:
	Employee compensation and benefit plans	$	16,629		$	527
	Fixed assets and other amortizable assets	90,130			3,742
	Reserves	4,362			—
	Valuation of investments	31,154			—
	Net operating loss carryforwards, net	125,728			1,041
	Less: Valuation allowance on net operating loss carryforwards	(36,043		)	—
	Total deferred tax assets	$	231,960		$	5,310
	Deferred tax liabilities
	Employee compensation and benefit plans	$	—		$	502
	Fixed assets and other amortizable assets	29,077			2,558
	Valuation of investments	10,414			1,831
	Reduction in foreign tax credit for Non-U.S. NOL carryforwards	18,885			—
	Total deferred tax liabilities	58,376			4,891
	Net deferred tax assets	$	173,584		$	419
	At December 31, 2013, the Company’s net deferred tax asset of $173.6 million was included in Deferred tax asset, net on the Consolidated Statements of Financial Condition. At December 31, 2012, the Company’s net deferred tax asset of $0.4 million was reported on the Consolidated Statements of Financial Condition as a deferred tax asset of $4.2 million and a liability within Accrued expenses and other liabilities of $3.8 million.
	Based on the weight of the positive and negative evidence considered, management believes that it is more likely than not that the Company will be able to realize its federal deferred tax assets in the future, and therefore no valuation allowance has been recorded at December 31, 2013. Management believes that positive evidence including the Company's history of sustainable profitability and its forecasts of future profitability outweighs the negative evidence. The Company has recorded a full valuation allowance against state and local deferred tax assets as it is more likely than not that the benefit of such items will not be realized due to limitations on utilization in the particular jurisdictions in which the Company operates.
	Included in the Company’s deferred tax assets are benefits associated with NOL carryforwards generated by Knight in periods prior to the Mergers. At December 31, 2013, the Company had projected overall U.S. federal NOL carryforwards of $194.5 million of which $89.0 million resulted from the acquisition of Knight. The Company recorded a related deferred income tax asset for $68.1 million and an offsetting valuation allowance of $6.8 million at December 31, 2013, which represents the portion of these net operating loss carryforwards that are considered more likely than not to expire unutilized. The Company did not have any NOLs or related deferred tax assets at December 31, 2012.
	In accordance with Section 382 of the Internal Revenue Code, a change in equity ownership of greater than 50% of a corporation within a three-year period results in an annual limitation on the corporation’s ability to utilize its NOL carryforwards that were created during tax periods prior to the change in ownership. As a result of the Mergers as well as prior ownership changes, Knight experienced ownership changes under Section 382 and as a result, the rate of utilization of NOL carryforwards generated by Knight may be limited. The Company does not believe these limitations will have a significant effect on the Company's ability to utilize its anticipated federal NOL carryforward. The Company's U.S. federal NOL carryforwards will begin to expire in 2019.
	At December 31, 2013 the Company recorded a valuation allowance for substantially all of its state and local NOL carryforwards as it is more likely than not that the benefit of such items will not be realized due to limitations on utilization in the particular jurisdictions in which the Company operates. Certain of these carryforwards are subject to annual limitations on utilization and they will begin to expire in 2019.
	At December 31, 2013, the Company had non-U.S. NOL carryforwards of $86.4 million of which $65.7 million were generated by Knight in periods prior to the Mergers. The Company recorded a foreign deferred income tax asset of $19.1 million for these NOL carryforwards as of December 31, 2013, along with an offsetting U.S. federal deferred tax liability of $18.9 million for the expected future reduction in U.S. foreign tax credits associated with the use of the non U.S. loss carryforwards. These non-U.S. net operating losses may be carried forward indefinitely. At December 31, 2013 the Company had tax credit carryforwards which were generated by Knight in periods prior to the Mergers, general business credit carryforwards of $2.5 million and alternative minimum tax credit carryforwards $6.8 million.
	At December 31, 2013, the Company had $1.5 million of unrecognized tax benefits, all of which would affect the Company's effective tax rate if recognized. The Company had no such unrecognized tax benefits at December 31, 2012 or December 31, 2011.
	The following table reconciles the beginning and ending amount of unrecognized tax benefits (in thousands):
		For the year ended December 31,
		2013
	Balance at beginning of period	$	—
	Increases based on tax positions related to prior periods (1)	1,464
	Decreases based on tax positions related to prior periods	—
	Decreases related to settlements with taxing authorities	—
Balance at the end of the period	$	1,464
(1) Increases relate to unrecognized tax benefits that inure to the Company as a result of the Mergers.
As of December 31, 2013, the Company is subject to U.S. Federal income tax examinations for the tax years 2009 through 2012, and to non U.S. income tax examinations for the tax years 2007 through 2012. In addition, the Company is subject to state and local income tax examinations in various jurisdictions for the tax years 2007 through 2012. The final outcome of these examinations is not yet determinable. However, the Company anticipates that adjustments to the unrecognized tax benefits, if any, will not result in a material change to the results of operations or financial condition.
The Company's policy for recording interest and penalties associated with audits is to record such items as a component of income or loss from continuing operations before income taxes. Penalties, if any, are recorded in Other expenses and interest paid or received is recorded in Interest expense and Interest, net, on the Consolidated Statements of Operations.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2013
Equity [Abstract]	'
Accumulated Other Comprehensive Income	'
	Accumulated Other Comprehensive Income
	The following table presents changes in Accumulated other comprehensive income, net of tax by component for the years ended December 31, 2012 and 2013 (in thousands):
		Unrealized Gains (Losses) on Available-for-Sale Securities			Foreign Currency Translation Adjustments		Total
	Balance January 1, 2012	$	—		$	—	$	—
	Other comprehensive income (loss)	114,319			—		114,319
	Balance December 31, 2012	114,319			—		114,319
	Other comprehensive income (loss)	13,689			1,365		15,054
	Reclassification of gain on investment in Knight Common Stock(1)	(127,972		)	—		(127,972		)
	Net current-period other comprehensive loss	(114,283		)	1,365		(112,918		)
	Balance December 31, 2013	$	36		$	1,365	$	1,401
	(1) As a result of the Mergers, the Company recorded a non-cash gain of $128.0 million on its investment in Knight Common Stock, which it recognized within Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013 and reversed any previous unrealized gains out of Other comprehensive income.

Writedowns_and_Other_Charges

Writedowns and Other Charges	12 Months Ended
	Dec. 31, 2013
Restructuring and Related Activities [Abstract]	'
Writedowns and Other Charges	'
	Writedowns and Other Charges
	Writedown of capitalized deal costs
	During the fourth quarter of 2013, the Company made a $300.0 million principal repayments related under the Credit Agreement. As a result, $13.2 million of capitalized deal costs were accelerated.
	Writedown of assets
	For the year ended 2013, the Company recorded $7.7 million in writedown of assets primarily related to leasehold improvements and office furniture in the London and Chicago office locations.
	Lease loss accrual
	For the year ended 2013, the Company recorded a $7.1 million lease loss accrual primarily related to the consolidation of office space in the London and Chicago.

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	Earnings Per Share
	Basic earnings or loss per common share (“EPS”) has been calculated by dividing net income from continuing operations by the weighted average shares of KCG Class A Common Stock outstanding during each respective period. Diluted EPS reflects the potential reduction in EPS using the treasury stock method to reflect the impact of common stock equivalents if stock options, SARs and warrants were exercised and restricted awards were to vest.
	The number of such options, warrants and SARs excluded was approximately 29.1 million for the year ended December 31, 2013. The computation of diluted shares can vary among periods due in part to the change in the average price of KCG Class A Common Stock.
	The following is a reconciliation of the numerators and denominators of the basic and diluted earnings per share computations from continuing operations for the years ended December 31, 2012 and 2011 (in thousands):
		For the year ended December 31,
		2013					2012				2011
		Numerator /			Denominator /		Numerator /		Denominator /		Numerator /		Denominator /
					shares		net		shares		net		shares
		net income					income				income
	Income from continuing operations and shares used in basic calculations	$	120,008		80,143		$	16,151	48,970		162,700		50,688
	Effect of dilutive stock based awards				872				—				—
	Income from continuing operations and shares used in diluted calculations	$	120,008		81,015		$	16,151	48,970		162,700		50,688
	(Loss) income from continuing operations allocated to preferred and participating units	$	(21,565	)			$	1,092			$	12,510
	Income from continuing operations attributable to common shareholders	$	141,573				$	15,059			$	150,190
	Basic earnings per common share from continuing operations				$	1.77			$	0.31			$	2.96
	Diluted earnings per common share from continuing operations				$	1.75			$	0.31			$	2.96
	Prior to the Mergers, GETCO units comprised preferred and common units, and net income was allocated among the various classes of units based upon participation rights in undistributed earnings. The number of shares used to calculate EPS for 2012 and 2011 are GETCO units converted into KCG shares using an exchange ratio as detailed in the Merger Agreement.

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingent Liabilities	'
	Commitments and Contingent Liabilities
	Legal Proceedings
	In the ordinary course of business, the nature of the Company’s business subjects it to claims, lawsuits, regulatory examinations and other proceedings. The Company and its subsidiaries are subject to several of these matters at the present time. Given the inherent difficulty of predicting the outcome of the litigation and regulatory matters, particularly in cases or proceedings in which substantial or indeterminate damages or fines are sought, or where cases or proceedings are in the early stages, the Company cannot estimate losses or ranges of losses for cases or proceedings where there is only a reasonable possibility that a loss may be incurred. In addition, there are numerous factors that result in a greater degree of complexity in class-action lawsuits as compared to other types of litigation. Due to the many intricacies involved in class-action lawsuits particularly in the early stages of such matters, obtaining clarity on a reasonable estimate is difficult which may call into question its reliability. There can be no assurance that these matters will not have a material adverse effect on the Company’s results of operations in any future period, and a material judgment could have a material adverse impact on the Company’s financial condition and results of operations. However, it is the opinion of management, after consultation with legal counsel that, based on information currently available, the ultimate outcome of these ordinary matters will not have a material adverse impact on the business, financial condition or operating results of the Company although they might be material to the operating results for any particular reporting period, depending, in part, upon operating results for that period. The Company, Knight and GETCO carry directors and officers liability insurance coverage for potential claims, including securities actions, against the Company, Knight and GETCO and their respective directors and officers.
	As previously disclosed in Knight's public filings, Knight experienced a technology issue at the open of trading at the NYSE on August 1, 2012. This issue was related to the installation of trading software and resulted in KCA sending numerous erroneous orders in NYSE-listed and NYSE Arca securities into the market. Knight has since been named as a defendant in two putative class action complaints (one of which was voluntarily dismissed) and one derivative lawsuit, all of which relate to the technology issue. Knight has also received several derivative demand letters and/or requests for the inspection or production of certain books and records pursuant to Delaware law related to the technology issue and the raising of $400.0 million in equity financing through a convertible preferred stock offering to certain investors (the "August 6, 2012 recapitalization").
	After the announcement on December 19, 2012 of the signing of the Merger Agreement, Knight, GETCO, GA-GTCO, as well as the individual members of the Knight's Board of Directors prior to the Mergers (the “Individual Defendants”), were named as defendants in several lawsuits brought by certain purported Knight stockholders challenging the proposed Mergers. The lawsuits generally allege, among other things, that the Mergers failed to properly value Knight, that the Individual Defendants breached their fiduciary duties in approving the Merger Agreement and that those breaches were aided and abetted by GETCO and GA-GTCO. The lawsuits, among other things, seek to enjoin the defendants from completing the Mergers on the agreed-upon terms, rescission of the Mergers (to the extent the Mergers have already been consummated), monetary relief and attorneys' fees and costs.
	While the Company is currently unable to predict the outcome of any existing or future litigation related to the August 1 technology issue, the August 6, 2012 recapitalization, or the Mergers, an unfavorable outcome in one or more of these matters could have a material adverse effect on its financial condition or ongoing results of operations. In addition, the Company expects to incur additional expenses in defending against such litigation.
	Legal
	Litigation Related to the August 1, 2012 Technology Issue
	On October 26, 2012, Knight, its Chairman and Chief Executive Officer, Thomas M. Joyce, and its Executive Vice President, Chief Operating Officer and Chief Financial Officer, Steven Bisgay, were named as defendants in an action entitled Fernandez v. Knight Capital Group, Inc. in the U.S. District Court for the District of New Jersey. Generally, this putative class action complaint alleged that the defendants made material misstatements and/or failed to disclose matters related to the events of August 1, 2012. The plaintiff asserted claims under Sections 10(b) and 20 and Rule 10b-5 of the federal securities laws, claiming that he and a purported class of Knight's stockholders who purchased Knight's Class A Common Stock between January 19, 2012 and August 1, 2012 paid an inflated price. Following the appointment of a lead plaintiff and counsel, the plaintiff filed an amended complaint on March 14, 2013, alleging generally that the defendants made material misstatements and/or failed to disclose matters related to the events of August 1, 2012. The plaintiff asserted claims under Sections 10(b) and 20 and Rule 10b-5 of the federal securities laws, claiming that it and a purported class of Knight's stockholders who purchased Knight's securities between November 30, 2011 and August 1, 2012 paid an inflated price. On May 13, 2013, Knight filed a motion to dismiss the amended complaint, which was fully briefed as of August 2013. Before the court rendered a decision on the motion to dismiss, the plaintiff filed a second amended complaint on December 20, 2013, alleging generally that the defendants made material misstatements and/or failed to disclose matters related to the events of August 1, 2012. More specifically, the plaintiff referred to the settlement with the SEC (discussed further below) and alleged that the defendants made false and misleading statements concerning Knight's risk management procedures and protocols, available cash and liquidity, Value at Risk and internal controls over financial reporting. The plaintiff asserted claims under Sections 10(b) and 20 and Rule 10b-5 of the federal securities laws, claiming that it and a purported class of Knight's stockholders who purchased Knight's securities between May 10, 2011 and August 1, 2012 paid an inflated price. The defendants filed a motion to dismiss the second amended complaint on February 18, 2014, and the motion is scheduled to be fully briefed by June 5, 2014.
	As noted above, Knight received several demand letters requesting that it commence a lawsuit against certain directors and officers for alleged breaches of fiduciary duties, waste, wrongdoing, mismanagement and/or demanding that it produce certain books and records pursuant to Delaware law concerning the technology issue and the August 6, 2012 recapitalization. The Company responded to each of these demand letters and, except as noted below in the New York litigation, none of these letters has resulted in litigation.
	Mergers Litigation
	Delaware Litigation. On December 28, 2012, a purported stockholder class action complaint was filed in the Court of Chancery of the State of Delaware, captioned Ann Jimenez McMillan v. Thomas M. Joyce, et al., Case No. 8163-VCP. The complaint names as defendants Knight, the Individual Defendants, GETCO, and GA-GTCO, LLC. The complaint generally alleges, among other things, that the Individual Defendants violated their fiduciary duties by accepting an inadequate merger price, approving the transaction despite material conflicts of interest, and agreeing to a number of improper deal protection devices and voting agreements, which allegedly make it less likely that other bidders would make successful competing offers for Knight. The complaint also alleges that Knight, GETCO, and GA-GTCO, LLC aided and abetted these purported breaches of fiduciary duties. The relief sought includes, among other things, an injunction prohibiting consummation of the Mergers, rescission of the Mergers (to the extent the Mergers have already been consummated), and attorneys' fees and costs. On December 28, 2012, a purported stockholder class action complaint was filed in the Court of Chancery of the State of Delaware, captioned Chrislaine Dominique v. Thomas M. Joyce, et al., Case No. 8159-VCP. The complaint names as defendants Knight, the Individual Defendants, GETCO, and GA-GTCO, LLC. The complaint generally alleges, among other things, that the Individual Defendants violated their fiduciary duties by accepting an inadequate merger price, approving the transaction despite material conflicts of interest, including that they were appointed by an investor group that included GETCO, and agreeing to a number of improper deal protection devices, which allegedly make it less likely that other bidders would make successful competing offers for Knight. The complaint also alleges that Knight and GETCO aided and abetted these purported breaches of fiduciary duties. The relief sought includes, among other things, an injunction prohibiting consummation of the Mergers, rescission of the Mergers (to the extent the Mergers have already been consummated), and attorneys' fees and costs. On January 31, 2013, the Court of Chancery consolidated for all purposes the McMillan and Dominique actions into a single action captioned In re Knight Capital Group, Inc. Shareholder Litigation, C.A. No. 8159-VCP. On March 5, 2013, the co-lead plaintiffs in the Delaware Consolidated Action filed an amended complaint and motions for expedited discovery and a preliminary injunction. In addition to the allegations in the initial complaints, the Delaware amended complaint contains allegations that the Knight Board of Directors breached its fiduciary duties by providing stockholders with allegedly deficient disclosures about the proposed transaction in the Company's Preliminary Form S-4, filed with the SEC on February 13, 2013 (the “Preliminary Proxy”).
	New Jersey Litigation. On December 31, 2012, a purported stockholder class action complaint was filed in the Superior Court of New Jersey, Chancery Division of Hudson County, NJ, captioned Charles Bryan v. Knight Capital, et al., Case No. HUD-C-001-13. The complaint names as defendants Knight, the Individual Defendants, Jefferies & Company, Inc., Jefferies High Yield Trading, LLC, TD Ameritrade Holding Corp., Blackstone Capital Partners VI L.P., Blackstone Family Investment Partnership VI-ESC L.P., Blackstone Family Investment Partnership VI L.P., Stephens Investments Holdings LLC, Stifel Financial Corp., GETCO Strategic Investments, LLC, GETCO Holding Company LLC, and GA-GTCO, LLC. The complaint generally alleges that the Individual Defendants breached their fiduciary duties by accepting an inadequate merger price, agreeing to a number of improper deal protection devices and voting agreements, which allegedly make it less likely that other bidders would make successful competing offers for Knight and approving the transaction despite material conflicts of interest, including that they were appointed by an investor group that included GETCO. The complaint further alleges that the entity defendants (except for Knight and GA-GTCO, LLC) breached alleged fiduciary duties in connection with the Individual Defendants' approval of the Mergers. The complaint also alleges that GETCO and GA-GTCO, LLC aided and abetted the Individual Defendants' purported breaches of fiduciary duty. The relief sought includes, among other things, an injunction prohibiting the consummation of the Mergers, rescission of the Mergers (to the extent the Mergers have already been consummated), and attorneys' fees and costs.
	On December 31, 2012, a purported stockholder class action complaint was filed in the Superior Court of New Jersey, Chancery Division of Hudson County, NJ, captioned James Ward v. Knight Capital, et al., Case No. HUD-C-0003-13. The complaint names as defendants Knight, the Individual Defendants, Jefferies & Company, Inc., Jefferies High Yield Trading, LLC, TD Ameritrade Holding Corp., Blackstone Capital Partners VI L.P., Blackstone Family Investment Partnership VI-ESC L.P., Blackstone Family Investment Partnership VI L.P., Stephens Investments Holdings LLC, Stifel Financial Corp., GETCO Strategic Investments, LLC, GETCO Holding Company LLC, and GA-GTCO, LLC. The complaint generally alleges that the Individual Defendants breached their fiduciary duties by accepting an inadequate merger price, agreeing to a number of improper deal protection devices and voting agreements, which allegedly make it less likely that other bidders would make successful competing offers for Knight and approving the transaction despite material conflicts of interest, including that they were appointed by an investor group that included GETCO. The complaint further alleges that the entity defendants (except for Knight and GA-GTCO, LLC) breached alleged fiduciary duties in connection with the Individual Defendants' approval of the Mergers. The complaint also alleges that GETCO and GA-GTCO, LLC aided and abetted the Individual Defendants' purported breaches of fiduciary duty. The relief sought includes, among other things, an injunction prohibiting the consummation of the Mergers, rescission of the Mergers (to the extent the Mergers have already been consummated), and attorneys' fees and costs. On February 20, 2013, Knight moved to dismiss or, in the alternative, stay the New Jersey actions in deference to the first-filed Delaware actions. The New Jersey court granted the motion on March 28, 2013, and ordered that the New Jersey actions be stayed for all purposes in deference to the first-filed Delaware actions.
	New York Litigation. On January 15, 2013, Knight, the Individual Defendants, GETCO, GA-GTCO, LLC and General Atlantic were named as defendants in an action entitled Joel Rosenfeld v. Thomas M. Joyce, et al., Case No. 6540147/2013, in the Supreme Court of the State of New York (New York County). The plaintiff, Joel Rosenfeld, is one of the stockholders mentioned above who previously sent Knight a derivative demand letter. Generally, this complaint asserts both derivative and class action claims. First, it purports to assert derivative claims, which allege, among other things, that the seven Knight directors who were serving as of August 1, 2012 breached their fiduciary duties and wasted corporate assets by failing to erect and oversee effective safeguards to prevent against technology issues, such as the one that occurred on August 1, 2012, for which Knight incurred a realized pre-tax loss of approximately $457.6 million. Second, it asserts putative class action claims resulting from the proposed Mergers for (1) breach of fiduciary duty against the Individual Defendants; and (2) aiding and abetting the purported breach of fiduciary duty against GETCO, GA-GTCO, LLC, and General Atlantic. The complaint generally alleges that the Individual Defendants breached their fiduciary duties by approving the Mergers at an inadequate price, agreeing to a number of improper deal protection devices and voting agreements, which allegedly make it less likely that other bidders would make successful competing offers for Knight, and that certain of Knight's directors have conflicts of interest in connection with the transaction, including that certain directors sought to enter into the transaction to avoid potential liability relating to the derivative claims asserted in the complaint. With respect to the merger claims, the plaintiff seeks, among other things, to enjoin the proposed Mergers, rescission of the proposed Mergers (to the extent they have already been consummated) and attorneys' fees. With respect to the derivative claims, the plaintiff seeks, among other things, an order requiring the Knight directors who were serving as of August 1, 2012 to pay restitution and/or compensatory damages in favor of Knight and/or the proposed class of Knight stockholders. On March 14, 2013, the plaintiff filed an amended complaint, which, in addition to the allegations in the initial complaint, contains allegations that the Knight Board of Directors breached its fiduciary duties by providing stockholders with allegedly deficient disclosures about the proposed transaction in the Preliminary Proxy. On March 21, 2013, the plaintiff moved by order to show cause for expedited discovery in support of his claims. The New York court issued an order on March 25, 2013, setting a hearing on the plaintiff's motion for April 4, 2013. On March 28, 2013, the parties in the New York action reached an agreement with respect to the matters raised in the plaintiff's motion and other aspects of the action, and as a result, on March 29, 2013, the plaintiff withdrew his motion for expedited discovery. On April 9, 2013, the New York court granted permission for the plaintiff to withdraw his motion.
	On June 10, 2013, the defendants entered into a memorandum of understanding with the plaintiffs in the Delaware shareholder actions and New York shareholder action regarding the settlement of those actions. In connection with the settlement, Knight and GETCO agreed to make supplemental disclosures to the joint proxy statement/prospectus filed with the SEC on May 28, 2013 (the “Proxy Statement”). In addition, Knight and GETCO agreed to make certain revisions to Knight's risk committee charter, as well as to KCG's risk committee charter.
	The memorandum of understanding contemplates that the parties will enter into a stipulation of settlement. The stipulation of settlement will be subject to customary conditions, including court approval following notice to Knight's former stockholders. In the event that the parties enter into a stipulation of settlement, a hearing will be scheduled at which the Delaware Court of Chancery will consider the fairness, reasonableness and adequacy of the settlement. If the settlement is finally approved by the court, it will resolve and release all claims that were brought or could have been brought in the Delaware, New York, and New Jersey shareholder actions, including claims challenging any aspect of the Mergers, the Merger Agreement, or any disclosure made in connection therewith, pursuant to terms that will be disclosed to Knight's former stockholders prior to final approval of the settlement. In addition, in connection with the settlement, the parties contemplate that plaintiffs' counsel will file a petition in the Delaware Court of Chancery for an award of attorneys' fees and expenses to be paid by KCG. There can be no assurance that the parties will enter into a stipulation of settlement, or that the court will approve any proposed settlement. In such event, the proposed settlement as contemplated by the memorandum of understanding may be terminated.
	The settlement is not, and should not be construed as, an admission of wrongdoing or liability by any of the defendants. The defendants continue to believe that the shareholder actions challenging the Mergers are without merit and vigorously deny the allegations that Knight's directors breached their fiduciary duties. Likewise, defendants do not believe that any disclosures regarding the Mergers are required under applicable laws other than that which have already been provided in the Proxy Statement. Nonetheless, the defendants entered into the memorandum of understanding to avoid the risk of the putative stockholder class action delaying or adversely affecting the Mergers, to minimize the substantial expense, burden, distraction and inconvenience of continued litigation and to fully and finally resolve the claims in the shareholder actions.
	Regulatory
	On or about August 9, 2012, the SEC began an examination of KCA's compliance with SEC Rule 15c3-5 (the “Market Access Rule”) and other rules and regulations as they relate to the August 1, 2012 technology issue. The SEC issued a formal order of investigation concerning Knight and KCA on August 29, 2012.
	On October 16, 2013, KCA reached a settlement with the SEC. KCA, without admitting or denying the findings, consented to the issuance of an administrative order relating to controls and procedures required by Section 15(c)(3) of the Securities Exchange Act of 1934 and SEC Rule 15c3-5 (the “Market Access Rule”), and Rules 200(g) and 203(b) of Regulation SHO (the “Short Sale Rules”). Under the terms of the settlement, KCA was censured, paid a civil penalty in the sum of $12.0 million and is required to cease and desist from committing future violations of the Market Access Rule and the Short Sale Rules. KCA was also required to retain an independent consultant to conduct a comprehensive review of KCA’s compliance with the Market Access Rule. The settlement resolved the SEC’s investigation relating to the August 1, 2012 technology issue. The full amount of this settlement had been accrued on Knight's July 1, 2013 balance sheet acquired by the Company.
	Other Legal and Regulatory Matters
	We own subsidiaries including regulated entities that are subject to extensive oversight under federal, state and applicable international laws as well as SRO rules. Changes in market structure and the need to remain competitive require constant changes to our systems and order handling procedures. We make these changes while continuously endeavoring to comply with many complex laws and rules. Compliance, surveillance and trading issues common in the securities industry are monitored by, reported to, and/or reviewed in the ordinary course of business by our regulators in the U.S. and abroad. As a major order flow execution destination, we are named from time to time in, or are asked to respond to a number of regulatory matters brought by U.S. regulators, foreign regulators and SROs that arise from our business activities. We are currently the subject of various regulatory reviews and investigations. In some instances, these matters may rise to a disciplinary action and/or civil or administrative action.
	In the second quarter of 2012, Knight recorded pre-tax trading losses of $35.4 million related to the Facebook IPO. On August 1, 2012 Nasdaq’s proposed voluntary accommodation program (the “Accommodation Program”) was published in the Federal Register by the SEC. The Accommodation Program creates a fund for voluntary accommodations for qualifying Nasdaq members disadvantaged by problems that arose during the Facebook IPO. Under the Accommodation Program as proposed by Nasdaq, Knight would recover a portion of its pre-tax trading losses. The Accommodation Program was approved by the SEC on March 22, 2013 which would allow Nasdaq to compensate market participants for certain claims related to system difficulties in connection with the Facebook IPO in an amount not to exceed $62.0 million. On April 2, 2013, Knight submitted an accommodation claim to Nasdaq. On October 25, 2013, Nasdaq provided the Company with notice that it had completed its review of the Company’s accommodation claim. On December 31, 2013, the Company received payment from Nasdaq totaling approximately $12.0 million comprising approximately $10.5 million to the Company and approximately $1.5 million which was rebated to customers in February 2014.
	Lease and Contract Obligations
	Capital Leases
	During 2012, the Company entered into capitalized lease obligations related to certain computer equipment. These obligations represent drawdowns under a revolving secured lending facility with a single lender. At December 31, 2013, the obligations have a weighted-average interest rate of 3.85% per annum and are on varying 3-year terms. The carrying amounts of the capital leases approximate fair value. The future minimum payments including interest under the capitalized leases at December 31, 2013 consist of (in thousands):
			Minimum Payments
	2014		8,222
	2015		2,072
	Total		$	10,294
	The total interest expense related to capital leases for the years ended December 31, 2013, 2012 and 2011 included in the Consolidated Statements Operations is as follows (in thousands):
		For the year ended December 31,
		2013			2012		2011
	Interest expense - Capital leases	$	700		$	1,376	$	982
	Operating Leases
	The Company leases office space under noncancelable operating leases. Certain office leases contain fixed dollar-based escalation clauses. Rental expense from continuing operations under the office leases was $16.0 million and $9.0 million for the year ended December 31, 2013 and 2012, respectively, and is included in Occupancy and equipment rentals on the Consolidated Statements of Operations.
	The Company leases certain computer and other equipment under noncancelable operating leases. As of December 31, 2013, future minimum rental commitments under all noncancelable office, computer and equipment leases (“Gross Lease Obligations”), and Sublease Income were as follows (in thousands):
		Gross Lease			Sublease		Net Lease
		Obligations			Income		Obligations
	Year ending December 31, 2014	$	29,689		$	4,315	$	25,374
	Year ending December 31, 2015	27,915			4,914		23,001
	Year ending December 31, 2016	27,571			4,850		22,721
	Year ending December 31, 2017	27,036			4,426		22,610
	Year ending December 31, 2018	26,492			2,720		23,772
	Thereafter through December 31, 2027	75,552			12,521		63,031
	Total	$	214,255		$	33,746	$	180,509
	Contract Obligations
	During the normal course of business, the Company collateralizes certain leases or other contractual obligations through letters of credit or segregated funds held in escrow accounts. At December 31, 2013, the Company had provided a letter of credit for $1.0 million, collateralized by U.S. Treasury Bills, as a guarantee for one of the Company’s lease obligations. In the ordinary course of business, KCG also has provided, and may provide in the future, unsecured guarantees with respect to the payment obligations of certain of its subsidiaries under trading, repurchase, financing and stock loan arrangements, as well as under certain leases.

Significant_Clients

Significant Clients	12 Months Ended
	Dec. 31, 2013
Risks and Uncertainties [Abstract]	'
Significant Clients	'
	Significant Clients
	The Company considers significant clients to be those clients who account for 10% or more of the total U.S. equity dollar value traded by the Company. No clients accounted for more than 10% of the Company’s U.S. equity dollar value traded for the years ended December 31, 2013, 2012 or 2011.

Net_capital_requirements

Net capital requirements	12 Months Ended
	Dec. 31, 2013
Brokers and Dealers [Abstract]	'
Net capital requirements	'
	Net capital requirements
	The Company's U.S. registered broker dealers are subject to the SEC’s Uniform Net Capital Rule, which requires the maintenance of minimum net capital. In 2013, the Company's U.S. registered broker dealers were in compliance with its capital adequacy requirements.
	The following table sets forth the net capital levels and requirements for the Company’s U.S. registered broker dealer subsidiaries at December 31, 2013 as filed in their respective regulatory filings (in thousands):
	Entity	Net Capital		Net Capital		Excess Net
				Requirement		Capital
	Knight Capital Americas LLC	$	396,655	$	22,300	$	374,355
	OCTEG, LLC	98,737		1,000		97,737
	GETCO Execution Services, LLC	11,433		250		11,183
	As of January 1, 2014, OCTEG was merged with and into KCA and KCA was renamed KCG Americas LLC. At the end of 2013, GETCO Execution Services, LLC submitted its application to withdraw its membership as a U.S. registered broker dealer.
	The Company’s foreign registered broker dealers are subject to certain financial resource requirements of either the FCA or the SFC. The following table sets forth the financial resource requirement for the following significant foreign regulated broker dealers at December 31, 2013 (in thousands):
	Entity	Financial		Resource		Excess
		Resources		Requirement		Financial
						Resources
	GETCO Europe Limited	$	157,254	$	80,900	$	76,354
	KCG Europe Limited	97,892		65,967		31,927

Financial_instruments_with_Off

Financial instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk	12 Months Ended
	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Financial instruments with off-balance sheet risk and concentrations of credit risk	'
	Financial instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk
	As a market maker in global equities, fixed income, futures, options, commodities and foreign currencies, the majority of the Company’s securities transactions are conducted as principal or riskless principal with broker dealers and institutional counterparties primarily located in the United States. The Company self-clears substantially all of its U.S. equity and option securities transactions. The Company clears a portion of its securities transactions through third party clearing brokers. Foreign transactions are settled pursuant to global custody and clearing agreements with major U.S. banks. Substantially all of the Company’s credit exposures are concentrated with its clearing brokers, broker dealer and institutional counterparties. The Company’s policy is to monitor the credit standing of counterparties with which it conducts business.
	The Company, through its FCM, also provides execution and clearing services in futures and options on futures contracts to facilitate customer transactions on major U.S. and European futures and options exchanges. Customer activities may expose the Company to off-balance sheet risk in the event the FCM customer is unable to fulfill its contracted obligation as the Company guarantees the performance of its clients to the respective clearing houses or other brokers. In accordance with regulatory requirements and market practice, the Company requires its customers to meet, at a minimum, the margin requirements established by each of the exchanges at which contracts are traded. Margin is a good faith deposit from the customer that reduces risk to the Company of failure by the customer to fulfill obligations under these contracts. The Company establishes customer credit limits and monitors required margin levels on a daily basis and, pursuant to such guidelines, require customers to deposit additional collateral, or to reduce positions, when necessary. Further, the Company seeks to reduce credit risk by entering into netting agreements with customers, which permit receivables and payables with such customers to be offset in the event of a customer default. Management believes that the margin deposits and collateral held at December 31, 2013 were adequate to minimize the risk of material loss that could be created by positions held at that time.
	In the normal course of its operations, the Company enters into contracts that contain a variety of representations and warranties which provide general indemnifications. The Company’s maximum exposure under these arrangements is unknown, as this would involve future claims that may be made against the Company that have not yet occurred. However, based on experience, the Company believes the risk of significant loss is minimal.
	Financial instruments sold, not yet purchased, at fair value represent obligations to purchase such securities (or underlying securities) at a future date. The Company may incur a loss if the market value of the securities subsequently increases.
	The Company currently has no loans outstanding to any former or current executive officer or director.

Business_Segments

Business Segments	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Business Segments	'
	Business Segments
	As of December 31, 2013, the Company's operating segments comprised the following: (i) Market Making; (ii) Global Execution Services; and (iii) Corporate and Other.
	The Market Making segment principally consists of market making in the cash, futures and options markets across global equities, options, fixed income foreign currencies and commodities. As a market maker, the Company commits capital on a principal basis by offering to buy securities from, or sell securities to, broker dealers, institutions and banks. Principal trading in the Market Making segment primarily consists of direct-to-client and non-client exchange-based electronic market making, including trade executions conducted as an equities DMM on the NYSE and NYSE Amex. The Company is an active participant on all major global equity and futures exchanges and also trades on substantially all domestic electronic options exchanges. As a complement to electronic market making, the Company’s cash trading business handles specialized orders and also transacts on the OTC Bulletin Board, marketplaces operated by the OTC Markets Group Inc. and the AIM of the London Stock Exchange.
	The Global Execution Services segment comprises agency execution services and trading venues, offering trading in global equities, options, foreign exchange, fixed income and futures to institutions, banks and broker dealers. The Company generally earns commissions as an agent between principals to transactions that are executed within this segment, however, the Company will commit capital on behalf of clients as needed. Agency-based, execution-only trading in the segment primarily consists of self-directed trading in global equities through a suite of algorithms or via an execution management system; institutional high touch sales traders executing program, block and riskless principal trades in global equities and ETFs; an institutional spot foreign exchange ECN; a fixed income ECN that also offers trading applications; an ATS for global equities; and futures execution and clearing through a FCM.
	The Corporate and Other segment prinicipally invests in strategic financial services-oriented opportunities, allocates, deploys and monitors all capital, and maintains corporate overhead expenses and all other income and expenses that are not attributable to the other segments, including the gain recognized on Knight Common Stock. The Corporate and Other segment also contains functions that support the Company’s other segments such as self-clearing services, including stock lending activities.
	The Company’s revenues, income (loss) from continuing operations before income taxes (“Pre-tax earnings”) and total assets by segment are summarized in the following table (in thousands):
		Market		Global Execution Services			Corporate			Consolidated
		Making					and Other			Total
	For the year ended December 31, 2013:
	Revenues	$	688,197	$	197,766		$	134,208		$	1,020,171
	Pre-tax earnings	103,559		(25,739		)	(60,007		)	17,813
	Total assets	3,939,965		1,106,448			1,944,802			6,991,215
	For the year ended December 31, 2012:
	Revenues	$	495,427	$	36,211		$	19,596		$	551,234
	Pre-tax earnings	34,887		(7,330		)	(1,130		)	26,427
	Total assets	1,408,516		33,623			245,397			1,687,536
	For the year ended December 31, 2011:
	Revenues	$	862,760	$	27,599		$	25,089		$	915,448
	Pre-tax earnings	203,886		(15,406		)	5,061			193,541
	Total assets	1,191,724		19,928			90,703			1,302,355
	The Company operates in the U.S. and internationally, primarily in Europe and Asia. The following table presents Revenues by geographic area.
		U.S.		International			Consolidated
							Total
	For the year ended December 31, 2013:
	Revenues	$	827,245	$	192,926		$	1,020,171
	For the year ended December 31, 2012:
	Revenues	$	340,117	$	211,117		$	551,234
	For the year ended December 31, 2011:
	Revenues	$	489,514	$	425,934		$	915,448

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	Subsequent Events
	Principal repayment under Credit Agreement
	On January 22, 2014, the Company made a $100.0 million principal repayment under the Credit Agreement and will record an additional $4.2 million in writedown of capitalized debt issuance cost in the first quarter of 2014. Including this payment, the Company has completed $400.0 million in principal repayments since entering into the Credit Agreement on July 1, 2013, fully satisfying the amortization payment of $235.0 million due on July 1, 2014 leaving a remaining outstanding balance of $135.0 million.
	Merger of BATS and Direct Edge
	In January 2014, BATS Global Markets Inc. and Direct Edge Holdings LLC announced plans to pay certain dividends to shareholders contingent on the completion of their pending merger. As a shareholder in both BATS and Direct Edge, KCG received approximately $41.7 million from the aggregate distributions paid at the close of the merger, which was closed as of January 31, 2014. The Company is currently assessing the treatment of these distributions for financial reporting purposes.

Condensed_Financial_Statements

Condensed Financial Statements of Knight Capital Group, Inc. (parent only)	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Condensed Financial Statements of Knight Capital Group, Inc. (parent only)	'
	Condensed Financial Statements of KCG Holdings, Inc. (parent only)
	Presented below are the Condensed Statements of Financial Condition, Operations and Cash Flows for the Company on an unconsolidated basis.
	Statements of Financial Condition
	KCG Holdings, Inc. (parent only)
		December 31,
		2013			2012
		(in thousands)
	Assets
	Cash and cash equivalents	$	253,017		$	114,511
	Financial instruments owned, at fair value	—			2
	Receivable from subsidiaries	60,460			216,266
	Investments in subsidiaries	1,356,412			773,818
	Goodwill and intangible assets, less accumulated amortization	—			8,132
	Income taxes receivable	90			—
	Deferred tax asset	144,109			—
	Subordinated loans to subsidiaries	250,000			—
	Other assets	21,182			1,039
	Total assets	$	2,085,270		$	1,113,768
	Liabilities & equity
	Liabilities
	Payable to subsidiaries	25,705			47,998
	Accrued expenses and other liabilities	12,313			84,959
	Debt	540,000			15,000
	Total liabilities	578,018			147,957
	Redeemable preferred member's equity	—			311,139
	Total equity	1,507,252			654,672
	Total liabilities & equity	$	2,085,270		$	1,113,768
	Statements of Operations
	KCG Holdings, Inc. (parent only)
		For the year ended December 31,
		2013			2012			2011
		(in thousands)
	Revenues
	Investment income and other, net	$	3,717		$	5,981		$	2,001
	Total revenues	3,717			5,981			2,001
	Expenses
	Employee compensation and benefits	31,970			(12,251		)	7,023
	Interest	28,476			1,195			256
	Depreciation and amortization	698			1,395			698
	Professional fees	30,488			4,997			1,484
	Bank fees	9,268			336			286
	Other	20,561			1,157			852
	Total expenses	121,461			(3,171		)	10,599
	(Loss) income before income taxes and equity in earnings of subsidiaries	(117,744		)	9,152			(8,598		)
	Income tax benefit	(120,761		)	—			—
	Income (loss) before equity in earnings of subsidiaries	3,017			9,152			(8,598		)
	Equity in earnings of subsidiaries	117,071			6,999			171,298
	Net income	$	120,088		$	16,151		$	162,700
	Statements of Cash Flows
	KCG Holdings, Inc. (parent only)
		For the year ended December 31,
		2013			2012			2011
		(In thousands)
	Cash flows from operating activities
	Net income	$	120,088		$	16,151		$	162,700
	Adjustments to reconcile net income to net cash used in operating activities
	Equity in earnings of subsidiaries	(117,071		)	(6,999		)	(171,298		)
	Writedown and amortization of debt issuance costs	16,931			52			—
	Amortization of intangibles	698			1,395			698
	Decrease (increase) in operating assets
	Subordinated loan receivable	(250,000		)	—			—
	Receivable from subsidiaries	(67,523		)	(97,375		)	(89,814		)
	Deferred tax asset	(144,109		)	—			—
Income taxes receivable	(90		)	—			—
Other assets	(15,351		)	31,031			48,653
(Decrease) increase in operating liabilities
Payable to subsidiaries	(2,024		)	11,756			33,932
Accrued expenses and other liabilities	59,921			5,106			718
Net cash used in operating activities	(398,530		)	(38,883		)	(14,411		)
Cash flows from investing activities
Cash acquired upon acquisition of Knight Capital Group, Inc.	509,133			—			—
Cash received from sale of Urban Financial of America, LLC	85,406			—			—
Acquisition of Automat Limited	—			—			(10,975		)
Dividends received from subsidiaries	646,425			161,606			127,530
Capital contributions to subsidiaries	(238,909		)	(70,794		)	(84,928		)
Net cash provided by investing activities	1,002,055			90,812			31,627
Cash flows from financing activities
Proceeds from issuance of Credit Agreement	535,000			—			—
Partial repayment of Credit Agreement	(300,000		)	—			—
Proceeds from issuance of Senior Secured Notes	305,000			—			—
Proceeds from issuance of notes payable	—			—			15,000
Repayment of notes payable	(15,000		)	—			—
Payment of debt issuance costs	(34,952		)	—			—
Issuance of equity to General Atlantic	55,000			—			—
Payment to former Knight Capital Group, Inc. stockholders	(720,000		)	—			—
Repayment of Knight Convertible Notes	(257,741		)	—			—
Funding of collateral account for Knight Convertible Notes	(117,259		)	—			—
Payment out of collateral account for Knight Convertible Notes	117,259			—			—
Proceeds from stock issuance	—			12,320			41,365
Member distributions	(21,002		)	(62,234		)	(124,791		)
Cost of common stock repurchased	(11,324		)	—			—
Net cash (used in) provided by financing activities	(465,019		)	(49,914		)	(68,426		)
Increase in cash and cash equivalents	138,506			2,015			(51,210		)
Cash and cash equivalents at beginning of period	114,511			112,496			163,706
Cash and cash equivalents at end of period	$	253,017		$	114,511		$	112,496
Supplemental disclosure of cash flow information:							—
Cash paid for interest	$	26,239		$	1,116		$	92
Cash paid for income taxes	$	365		$	—		$	—
The condensed financial statements of KCG Holdings, Inc. (parent only; the “Parent Company”) should be read in conjunction with the Consolidated Financial Statements of the Company and the Notes thereto. As noted in Footnote 1 "Organization and Description of Business", the Mergers were treated as a purchase of Knight by GETCO for accounting and financial reporting purposes.
The Statements of Operations and Cash Flows included in this footnote for the year ended December 31, 2013 include the combined financial results and cash flows for GETCO Holding Company, LLC for the six month period January 1, 2013 to June 30, 2013 and for KCG Holdings, Inc. for the six month period July 1, 2013 to December 31, 2013. These combined Statements of Operations and Cash Flows were presented for comparability to the prior years, 2012 and 2011. The Statement of Financial Condition at December 31, 2013 represents the financial condition of the Parent Company. The Statement of Financial Condition at December 31, 2012 represents the financial condition of GETCO Holding Company, LLC.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of consolidation and form of presentation	'
	Basis of consolidation and form of presentation
	The Consolidated Financial Statements, prepared in conformity with GAAP, include the accounts of the Company and its subsidiaries. All significant intercompany transactions and balances have been eliminated.
	Certain reclassifications have been made to the prior periods’ Consolidated Financial Statements in order to conform to the current period presentation. Such reclassifications are immaterial to both current and all previously issued financial statements taken as a whole and have no effect on previously reported Consolidated Net income.
Cash and cash equivalents	'
	Cash and cash equivalents
	Cash and cash equivalents include money market accounts, which are payable on demand, and short-term investments with an original maturity of less than 90 days. The carrying amount of such cash equivalents approximates their fair value due to the short-term nature of these instruments.
Cash and securities segregated under federal and other regulations	'
	Cash and securities segregated under federal and other regulations
	The Company maintains custody of customer funds and is obligated by rules and regulations mandated by the U.S. Securities and Exchange Commission (“SEC”) and the Commodities Futures Trading Commission (“CFTC”) to segregate or set aside cash and/or qualified securities to satisfy these regulations, which have been promulgated to protect customer assets. The amounts recognized as Cash and securities segregated under federal and other regulations approximate fair value.
Market making, sales, trading and execution activities	'
	Market making, sales, trading and execution activities
	Financial instruments owned and Financial instruments sold, not yet purchased, relate to market making and trading activities, include listed and other equity securities, listed equity options and fixed income securities which are recorded on a trade date basis and carried at fair value. Trading revenues, net, which comprises trading gains, net of trading losses, are also recorded on a trade date basis.
	Commissions, which includes commission equivalents earned on institutional client orders and commissions on futures transactions, and related expenses are also recorded on a trade date basis. Commissions earned by the Company’s FCM are recorded net of any commissions paid to independent brokers and are recognized on a half-turn basis.
Fair value of financial instruments	'
	Fair value of financial instruments
	The Company values its financial instruments using a hierarchy of fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value.
	The fair value hierarchy can be summarized as follows:
	•	Level 1—Valuations based on quoted prices in active markets for identical assets or liabilities that the Company has the ability to access. Since valuations are based on quoted prices that are readily and regularly available in an active market, valuation of these products does not entail a significant degree of judgment.
	•	Level 2—Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly.
	•	Level 3—Valuations based on inputs that are unobservable and significant to the overall fair value measurement.
	Changes in fair value are recognized in earnings each period for financial instruments that are carried at fair value. See Footnote 6 “Fair Value of Financial Instruments” for a description of valuation methodologies applied to the classes of financial instruments at fair value.
Collateralized agreements and financings	'
	Collateralized agreements and financings
	Collateralized agreements consist of securities borrowed and collateralized financings include securities loaned and financial instruments sold under agreements to repurchase.
	•	Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral advanced or received. Securities borrowed transactions facilitate the securities settlement process and require the Company to deposit cash or other collateral with the lender. Securities loaned transactions help finance the Company’s securities inventory whereby the Company lends stock to counterparties in exchange for the receipt of cash or other collateral from the borrower. In these transactions, the Company receives or lends cash or other collateral in an amount generally in excess of the market value of the applicable securities borrowed or loaned. The Company monitors the market value of securities borrowed or loaned on a daily basis, and obtains additional collateral or refunds excess collateral as necessary.
	•	Financial instruments sold under agreements to repurchase are used to finance inventories of securities and other financial instruments and are recorded at their contractual amount. The Company has entered into bilateral and tri-party term and overnight repurchase agreements which bear interest at negotiated rates. The Company receives cash and makes delivery of financial instruments to a custodian who monitors the market value of these instruments on a daily basis. The market value of the instruments delivered must be equal to or in excess of the principal amount loaned under the repurchase agreements plus the agreed upon margin requirement. The custodian may request additional collateral, if appropriate.
	The Company’s securities borrowed, securities loaned and financial instruments sold under agreements to repurchase are recorded at amounts that approximate fair value. These items are recorded based upon their contractual terms and are not materially sensitive to shifts in interest rates because they are short-term in nature and are fully collateralized. These items would be categorized as Level 2 in the fair value hierarchy if they were required to be recorded at fair value.
Securitization activities	'
	The Company’s securities borrowed, securities loaned and financial instruments sold under agreements to repurchase are recorded at amounts that approximate fair value. These items are recorded based upon their contractual terms and are not materially sensitive to shifts in interest rates because they are short-term in nature and are fully collateralized. These items would be categorized as Level 2 in the fair value hierarchy if they were required to be recorded at fair value.
Investments	'
	Investments
	Investments primarily comprise strategic noncontrolling equity ownership interests in financial services-related businesses and are held by the Company's non-broker dealer subsidiaries. These strategic investments are accounted for under either the equity method, at fair value or at cost. The equity method of accounting is used when the Company has significant influence. Strategic investments are held at cost, less impairment if any, when the investment does not have a readily determined fair value, and the Company is not considered to exert significant influence on operating and financial policies of the investee.
	Prior to the Mergers, GETCO had a strategic investment in Knight which was classified as available for sale and held at fair value with any unrealized gains or losses recorded in Other comprehensive income or loss. As a result of the Mergers, the Company recognized a non-cash gain of $128.0 million on its investment in Knight Common Stock, which it recorded within Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013 and reversed any previous unrealized gains out of Other comprehensive income.
	Strategic investments are reviewed on an ongoing basis to ensure that the carrying values of the investments have not been impaired. If the Company determines that an impairment loss on a strategic investment has occurred due to a decline in fair value or other market conditions, the investment is written down to its estimated fair value.
	The Company maintains a non-qualified deferred compensation plan for certain employees and directors. This plan provides a return to the participants based upon the performance of various investments. In order to hedge its liability under this plan, the Company generally acquires the underlying investments and holds such investments until the deferred compensation liabilities are satisfied. Changes in value of such investments are recorded in Investment income and other, net, with a corresponding charge or credit to Employee compensation and benefits on the Consolidated Statements of Operations. Deferred compensation investments primarily consist of mutual funds, which are accounted for at fair value.
Goodwill and intangible assets	'
	Goodwill and intangible assets
	The Company tests goodwill and intangible assets with an indefinite useful life for impairment annually or when an event occurs or circumstances change that signifies the existence of an impairment. The Company capitalizes certain costs associated with the acquisition or development of internal-use software and amortizes the software over its estimated useful life of three years, commencing at the time the software is placed in service. The Company amortizes intangible assets with a finite life on a straight line basis over their estimated useful lives and tests for recoverability whenever events indicate that the carrying amounts may not be recoverable.
Payable to customers	'
	Payable to customers
	Payable to customers arise primarily from futures transactions and include amounts due on cash and margin transactions. Due to their short-term nature, such amounts approximate fair value.
Treasury stock	'
	Treasury stock
	The Company records its purchases of treasury stock at cost as a separate component of stockholders’ equity. The Company may obtain treasury stock through purchases in the open market or through privately negotiated transactions. Certain treasury stock repurchases represent shares of KCG Class A Common Stock repurchased in satisfaction of tax withholding obligations upon vesting of restricted awards. The Company may re-issue treasury stock, at average cost, for the acquisition of new businesses or, in certain instances, as inducement grants to new hires.
Foreign currency translation and foreign currency forward contracts	'
	Foreign currency translation and foreign currency forward contracts
	The Company has foreign subsidiaries that do not utilize the U.S. dollar as their functional currency.
	Assets and liabilities of the foreign subsidiaries having non-U.S. dollar functional currencies are translated at exchange rates at the end of a period. Revenues and expenses are translated at average exchange rates during the period. Gains and losses resulting from translating foreign currency financial statements into U.S. dollars are included in Accumulated other comprehensive income on the Consolidated Statements of Financial Condition and Cumulative translation adjustment on the Consolidated Statements of Comprehensive Income. Gains or losses resulting from foreign currency transactions are included in Investment income and other, net on the Company’s Consolidated Statements of Operations. For the years ended December 31, 2013, 2012, and 2011 the Company recorded a loss of $4.1 million, a gain of $0.2 million and a loss of $2.4 million, respectively.
	The Company seeks to reduce the impact of fluctuations in foreign exchange rates on its net investment in certain non-U.S. operations through the use of foreign currency forward contracts. For foreign currency forward contracts designated as hedges, the Company assesses its risk management objectives and strategy, including identification of the hedging instrument, the hedged item and the risk exposure and how effectiveness is to be assessed prospectively and retrospectively. The effectiveness of the hedge is assessed based on the overall changes in the fair value of the forward contracts. For qualifying net investment hedges, any gains or losses, to the extent effective, are included in Accumulated other comprehensive income or loss on the Consolidated Statements of Financial Condition and the Consolidated Statements of Comprehensive Income. The ineffective portion, if any, is recorded in Investment income and other, net on the Consolidated Statements of Operations.
Stock-based compensation	'
	Stock and unit based compensation
	Stock and unit based compensation is measured based on the grant date fair value of the awards. These costs are amortized over the requisite service period, which is typically the vesting period. Expected forfeitures are considered in determining stock-based employee compensation expense.
	The Company applies a non-substantive vesting period approach for stock-based awards related to KCG Class A Common Stock whereby the expense is accelerated for those employees and directors that receive options, stock appreciation rights ("SARs") and RSUs and are eligible to retire prior to the vesting of such awards.
Soft dollar expense	'
	Soft dollar expense
	Under a commission management program, the Company allows institutional clients to allocate a portion of their gross commissions to pay for research and other services provided by third parties. As the Company acts as an agent in these transactions, it records such expenses on a net basis within Commissions and fees on the Consolidated Statements of Operations.
Depreciation, amortization and occupancy	'
	Depreciation, amortization and occupancy
	Fixed assets are depreciated on a straight-line basis over their estimated useful lives of three to seven years. Leasehold improvements are being amortized on a straight-line basis over the shorter of the term of the related office lease or the expected useful life of the assets.The Company reviews fixed assets and leasehold improvements for impairment whenever events or changes in circumstances indicate that the related carrying amounts may not be recoverable.
	The Company recognizes rent expense under operating leases with fixed rent escalations, lease incentives and free rent periods on a straight-line basis over the lease term beginning on the date the Company takes possession of or controls the use of the space, including during free rent periods.
Lease loss accrual	'
	Lease loss accrual
	The Company’s policy is to identify excess real estate capacity and where applicable, accrue for related future costs, net of estimated sub-lease income upon the date the Company ceases to use the excess real estate. In the event the Company is able to sublease the excess real estate after recording a lease loss, such accrual is adjusted to the extent the actual terms of sub-leased property differ from the assumptions used in the calculation of the accrual. In the event that the Company concludes that previously determined excess real estate is needed for the Company’s use, such lease loss accrual is adjusted accordingly.
Income taxes	'
	Income taxes
	Prior to the Mergers, GETCO and the majority of its subsidiaries were treated as partnerships or disregarded entities for U.S. income tax purposes and, accordingly, were not subject to federal income taxes. Instead, the former GETCO members were liable for federal income taxes on their proportionate share of taxable income. Upon completion of the Mergers, the Company became a corporation subject to U.S. corporate income taxes and, following the Mergers, the Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial reporting and tax bases of assets and liabilities and measures them using the enacted tax rates and laws that will be in effect when such differences are expected to reverse. The Company evaluates the recoverability of future tax deductions by assessing the adequacy of future expected taxable income from all sources, including reversal of temporary differences and forecasted operating earnings
Use of estimates	'
	Use of estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates.
Recently adopted accounting guidance	'
	Recently adopted accounting guidance
	In December 2011, the Financial Accounting Standards Board (“FASB”) issued an Accounting Standard Update (“ASU”) that requires additional disclosures about financial assets and liabilities that are subject to netting arrangements. Under the ASU, financial assets and liabilities must be disclosed at their respective gross asset and liability amounts, the amounts offset on the balance sheet and a description of the respective netting agreements. The new disclosures were required for reporting periods beginning on or after January 1, 2013, and are to be applied retrospectively. Other than requiring additional disclosures, the adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements.
	In February 2013, the FASB issued an ASU that requires additional disclosure requirements for items reclassified out of accumulated other comprehensive income. This new guidance requires entities to present either on the face of the income statement or in the notes to the financial statements the effects on the specific line items of the income statement for amounts reclassified out of accumulated other comprehensive income. This ASU was effective for reporting periods beginning after December 15, 2012. Other than additional disclosure requirements, the adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements.
	Recent accounting guidance to be adopted in future periods
	In March 2013, the FASB issued an ASU concerning the parent's accounting for the cumulative translation adjustment upon derecognition of certain subsidiaries or groups of assets within a foreign entity or of an investment in a foreign entity. This ASU provides for the release of the cumulative translation adjustment into net income when a parent sells a part or all of its investment within a foreign entity, no longer holds a controlling interest in an investment in a foreign entity or obtains control of an investment in a foreign entity that was previously recognized as an equity method investment. This ASU is effective for reporting periods beginning after December 15, 2013, however early adoption is permitted. The adoption of this ASU will not have an impact on the Company's Consolidated Financial Statements.
	In July 2013, the FASB issued an ASU to clarify the financial statement presentation of an unrecognized tax benefit when a NOL carryforward, a similar tax loss, or a tax credit carryforward exists. This ASU requires entities to present an unrecognized tax benefit as a reduction of a deferred tax asset for a NOL carryforward whenever the NOL or tax credit carryforward would be available to reduce the additional taxable income or tax due if the tax position is disallowed. The ASU is required for reporting periods beginning after December 15, 2013. Upon adoption, entities are required to apply the provisions of the ASU prospectively for all unrecognized tax benefits that exist at the adoption date, however, the ASU also indicates that retrospective application is permitted. The adoption of this ASU will not have an impact on the Company's Consolidated Financial Statements.

Merger_of_GETCO_and_Knight_Tab

Merger of GETCO and Knight (Tables)	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Schedule of Business Acquisitions, by Acquisition	'
	Amounts preliminarily allocated to intangible assets and goodwill, and the amortization period for intangible assets with finite useful lives, were as follows (dollars in thousands):
							Amortization
			Amount				Years
	Technology		$	110,504			5 years
	Customer relationships		35,000				9 - 11 years
	Trade names		4,000				10 years
	Trading rights (1)		5,921				7 years
	Intangible assets		155,425
	Goodwill		11,615
	Total		$	167,040
	The following table reflects the preliminary allocation of the purchase price to the assets acquired and liabilities assumed at the acquisition date (in thousands):
	Identifiable Net Assets
	Cash and cash equivalents				$	509,133
	Cash and securities segregated under federal and other regulations				203,045
	Financial instruments owned				1,937,929
	Securities borrowed				1,158,981
	Receivable from brokers, dealers and clearing organizations				1,369,474
	Fixed assets and leasehold improvements				80,280
	Investments				106,353
	Intangible assets				155,425
	Assets within discontinued operations				5,607,063
	Deferred tax asset, net				62,329
	Other assets				141,617
	Total Assets				$	11,331,629
	Financial instruments sold, not yet purchased				$	1,512,983
	Collateralized financings				1,166,211
	Payable to brokers, dealers and clearing organizations				635,914
	Payable to customers				527,918
	Accrued compensation expense				107,409
	Accrued expenses and other liabilities				126,507
	Liabilities within discontinued operations				5,518,168
	Long-term debt				375,000
	Total Liabilities				$	9,970,110
	Total identified assets acquired, net of assumed liabilities				1,361,519
	Goodwill				11,615
	Total Purchase Price				$	1,373,134
Business Acquisition, Pro Forma Information	'
	Included in KCG results for the year ended December 31, 2013 are results from the businesses acquired as a result of the Mergers as follows (in thousands):
		Year ended December 31,
		2013
	Revenues	$	486,119
	Income from continuing operations, before income taxes	54,070
	The following pro forma results are based on adding the pre-tax historical results of GETCO and Knight, and adjusting primarily for amortization of intangibles acquired in the Mergers, debt raised in conjunction with the Mergers and income taxes as if the Company was subject to U.S. corporate income taxes for all periods presented. The pro forma data assumes that no payments were made on the First Lien Credit Facility (as later defined) except those prescribed in the Credit Agreements (as later defined), that all GETCO units have been converted to KCG Class A Common Stock on January 1, 2012, and excludes any gain recognized on Knight Common Stock. The pro forma disclosures do not include adjustments to reflect the Company's operating costs or expected differences in the way funds generated by the Company are invested. The pro forma data is intended for informational purposes and is not indicative of the future results of operations.
			Year ended December 31, 2013							Year ended December 31, 2012
			Reported				Pro Forma (unaudited)			Reported		Pro Forma (unaudited)
			(in thousands, except per share amounts)
	Revenue		$	1,020,171			$	1,421,566		$	551,234	$	1,020,334
	Net income from continuing operations		120,008				(69,414		)	16,151		(286,656		)
	Net income		120,088				(98,394		)	16,151		(355,130		)
	Diluted earnings (loss) per common share from continuing operations		$	1.75			$	(0.86	)	$	0.31	$	(5.85	)
	Diluted earnings (loss) per common share		$	1.75			$	(1.21	)	$	0.31	$	(7.25	)

Significant_Accounting_Policie2

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Schedule of Interest Income and Interest Expense	'
	Interest income and interest expense which have been netted within Interest, net on the Consolidated Statements of Operations are as follows (in thousands):
		For the year ended December 31,
		2013			2012			2011
	Interest Income	$	10,187		$	3,070		$	1,131
	Interest Expense	(10,724		)	(5,427		)	(2,342		)
	Interest, net	$	(537	)	$	(2,357	)	$	(1,211	)
Net Trading Revenue Including Dividend Income and Expense	'
	Trading revenue, net includes dividend income and expense as follows (in thousands):
		For the year ended December 31,
		2013			2012			2011
	Dividend Income	$	26,237		$	2,253		$	4,700
	Dividend Expense	$	(21,630	)	$	(1,599	)	$	(1,512	)

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Summary of Revenues and Results of Operations of Discontinued Operations	'
	The revenues and results of operations of discontinued operations are summarized as follows (in thousands):
		For the six months ended December 31,
		2013
	Revenues	$	39,868
	Expenses:
	Compensation	$	14,068
	Execution and clearance fees	5,038
	Payments for order flow	9,885
	Other expenses	10,748
	Total Expenses	39,739
	Pre-tax income from discontinued operations	129
	Income tax expense	(49		)
	Income from discontinued operations, net of tax	$	80

Assets_Segregated_or_Held_in_S1

Assets Segregated or Held in Separate Accounts Under Federal or Other Regulations (Tables)	12 Months Ended
	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]	'
Cash and Securities Segregated Under U.S. Federal and Other Regulation	'
	Cash and securities segregated under U.S. federal and other regulations primarily relate to the Company’s FCM business and consist of the following (in thousands):
		December 31,
		2013
	Cash and cash equivalents segregated under federal or other regulations	$	183,083
	Receivables from brokers, dealers and clearing organizations (1)	304,294
	Total assets segregated or held in separate accounts under federal or other regulations	$	487,377

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	'
	The following fair value hierarchy table presents information about the Company’s financial assets and liabilities measured at fair value (in thousands):
		Assets and Liabilities Measured at
		Fair Value on a Recurring Basis
	31-Dec-13	Level 1				Level 2				Level 3				Total
	Assets
	Financial instruments owned, at fair value:
	Equities (1)	$	2,298,785			$	—			$	—			$	2,298,785
	Listed options	339,798				—				—				339,798
	U.S. government and Non-U.S. government obligations	40,053				—				—				40,053
	Corporate debt	43,203				—				—				43,203
	Total Financial instruments owned, at fair value	2,721,839				—				—				2,721,839
	Securities on deposit with clearing organizations (2)	170,235				—				—				170,235
	Investment in CME Group (3)	3,925				—				—				3,925
	Deferred compensation investments (3)	—				117				—				117
	Investment in Deephaven Funds (3)	—				1,958				—				1,958
	Total assets held at fair value	$	2,895,999			$	2,075			$	—			$	2,898,074
	Liabilities
	Financial instruments sold, not yet purchased, at fair value:
	Equities (1)	$	1,851,006			$	—			$	—			$	1,851,006
	Listed options	252,282				—				—				252,282
	U.S. government obligations	15,076				—				—				15,076
	Corporate debt	42,122				—				—				42,122
	Foreign currency forward contracts	—				5,014				—				5,014
	Total liabilities held at fair value	$	2,160,486			$	5,014			$	—			$	2,165,500
	________________________________________
	(1)	Equities of $697.9 million have been netted by their respective long and short positions by CUSIP number.
	(2)	Securities on deposit with clearing organizations consist of U.S. government obligations and are recorded within Receivable from brokers, dealers and clearing organizations on the Consolidated Statements of Financial Condition.
	(3)	Investment in CME Group, Deferred compensation investments and Investment in Deephaven Funds are included within Investments on the Consolidated Statements of Financial Condition.
		Assets and Liabilities Measured at
		Fair Value on a Recurring Basis
	31-Dec-12	Level 1				Level 2				Level 3				Total
	Assets
	Financial instruments owned, at fair value:
	Equities (1)	$	378,933			$	—			$	—			$	378,933
	Listed options	92,305				—				—				92,305
	U.S. government obligations and corporate bonds	68,765				—				—				68,765
	Mutual funds - Bond Funds	114,872				—				—				114,872
	Total Financial instruments owned, at fair value	654,875				—				—				654,875
	Securities on deposit with clearing organizations	7,147				—				—				7,147
	Investment in CME Group	3,040				—				—				3,040
	Investment in Knight preferred shares	199,632				—				—				199,632
	Total assets held at fair value	$	864,694			$	—			$	—			$	864,694
	Liabilities
	Financial instruments sold, not yet purchased, at fair value:
	Equities (1)	$	423,740			$	—			$	—			$	423,740
	Listed options	69,757				—				—				69,757
	U.S. government obligations	19,056				—				—				19,056
	Total Financial instruments sold, not yet purchased, at fair value	512,553				—				—				512,553
	Total liabilities held at fair value	$	512,553			$	—			$	—			$	512,553
	___________________________________
	(1) Equities of $5.9 million have been netted by their respective long and short positions by CUSIP number.
Fair Value of Derivative Instruments in Consolidated Statements of Financial Condition and Effect of Changes in Fair Value on Consolidated Statements of Operations	'
	The following tables summarize the fair value of derivative instruments and futures contract trading activities in the Consolidated Statements of Financial Condition and the gains and losses included in the Consolidated Statements of Operations (fair value in thousands):
				31-Dec-13
		Financial Statements		Assets							Liabilities
		Location		Fair Value				Contracts			Fair Value				Contracts
	Foreign currency
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		$	89			892			$	142			533
	Forward contracts (1)	Financial instruments owned, at fair value		6,913				1			11,515				2
	Equity
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		223				1,069			1,089				1,046
	Swap contracts	Receivables from/Payables to brokers, dealers and clearing organizations		—				—			18				1
	Listed options	Financial instruments owned, at fair value		339,798				730,020			252,282				755,947
	Fixed income
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		4,815				18,280			2,259				15,202
	Commodity
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		3,392				10,629			1,773				3,806
	Total			$	355,230			760,891			$	269,078			776,537
	(1) Designated as hedging instrument
				31-Dec-12
		Financial Statements		Assets							Liabilities
		Location		Fair Value				Contracts			Fair Value				Contracts
	Foreign currency
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		$	8			500			$	5			110
	Forward contracts	Accrued expenses and other liabilities		—				—			110				1
	Equity
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		270				766			477				1,070
	Swap contracts	Receivables from/Payables to brokers, dealers and clearing organizations		570				1			—				—
	Listed options	Financial instruments owned, at fair value		92,305				199,324			69,757				196,804
	Fixed income
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		449				49,498			2,014				53,882
	Commodity
	Futures contracts	Receivables from/Payables to brokers, dealers and clearing organizations		13				1,060			—				—
	Total			$	93,615			251,149			$	72,363			251,867
Fair Value of Derivative Instruments Gain Loss Recognized	'
					Gain (Loss) Recognized
			Financial Statements		For the year
					ended December 31,
			Location		2013				2012				2011
	Derivative instruments not designated as hedging instruments:
	Foreign currency
	Futures contracts		Trading revenues, net		$	12,191			$	19,699			$	25,808
	Equity
	Futures contracts		Trading revenues, net		50,073				76,089				156,537
	Swap contracts		Trading revenues, net		11,736				8,116				18,624
	Listed options (1)		Trading revenues, net		37,035				50,446				90,389
	Fixed income
	Futures contracts		Trading revenues, net		80,511				81,933				170,414
	Commodity
	Futures contracts		Trading revenues, net		62,215				35,952				24,154
					$	253,761			$	272,235			$	485,926
	Derivative instruments designated as hedging instruments:
	Foreign exchange - forward contract		Accumulated other comprehensive income		$	(3,298	)		$	—			$	—
	(1)	Realized gains and losses on listed equity options relate to the Company’s market making activities in such options. Such market making activities also comprise trading in the underlying equity securities with gains and losses on such securities generally offsetting the gains and losses reported in this table. Gains and losses on such equity securities are also included in Trading revenue, net on the Company’s Consolidated Statements of Operations.
Gross amounts of recognized derivative assets and gross amounts of offsets in the Consolidated Statement of Condition	'
	The gross amounts of assets and liabilities subject to netting and gross amounts offset in the Consolidated Statements of Financial Condition were as follows (in thousands):
		31-Dec-13	Gross Amounts Recognized				Gross Amounts Offset in the Statements of Financial Condition				Net Amounts of Assets Presented in the Statements of Financial Condition				Gross Amounts Not Offset in the Statement of Financial Condition				Net Amount
															Financial Instruments		Cash Collateral Received
		Assets
		Listed options	$	339,798			$	—			$	339,798			$	—	$	—	$	339,798
		Securities borrowed	1,357,387				—				1,357,387				1,326,220		—		31,167
		Receivable from brokers, dealers and clearing organizations (1)	24,366				—				24,366				24,249		—		117
		Foreign currency forward contracts	6,913				6,501				412				—		—		412
		Futures	8,519				4,369				4,150				—		—		4,150
		Total Assets	$	1,736,983			$	10,870			$	1,726,113			$	1,350,469	$	—	$	375,644
		Liabilities
		Listed options	$	252,282			$	—			$	252,282			$	—	$	10,924	$	241,358
		Securities loaned	733,230				—				733,230				726,948		—		6,282
		Financial instruments sold under agreements to repurchase	640,950				—				640,950				640,948		—		2
		Foreign currency forward contracts	11,515				6,501				5,014				—		—		5,014
		Futures	5,263				5,263				—				—		—		—
		Swaps	18				—				18				—		—		18
		Total Liabilities	$	1,643,258			$	11,764			$	1,631,494			$	1,367,896	$	10,924	$	252,674
	(1) Represent reverse repurchase agreements at broker dealer
		31-Dec-12	Gross Amounts Recognized				Gross Amounts Offset in the Statements of Financial Condition				Net Amounts of Assets Presented in the Statements of Financial Condition				Gross Amounts Not Offset in the Statement of Financial Condition				Net Amount
															Financial Instruments		Cash Collateral Received
		Assets
		Listed options	$	92,305			$	—			$	92,305			$	—	$	—	$	92,305
		Securities borrowed	52,261				—				52,261				50,717		—		1,544
		Futures	740				462				278				—		$	—	278
		Total Assets	$	145,306			$	462			$	144,844			$	50,717	$	—	$	94,127
		Liabilities
		Listed options	$	69,757			$	—			$	69,757			$	—	$	1,393	$	68,364
		Futures	2,497				2,497				—				—		—		—
		Total Liabilities	$	72,254			$	2,497			$	69,757			$	—	$	1,393	$	68,364

Collateralized_Transactions_Ta

Collateralized Transactions (Tables)	12 Months Ended
	Dec. 31, 2013
Collateralized Agreements [Abstract]	'
Financial Instruments at Fair Value Received as Collateral that were Permitted to be Delivered or Repledged	'
	The table below presents financial instruments at fair value received as collateral and included within Securities borrowed on the Consolidated Statements of Financial Condition that were permitted to be delivered or repledged and that were delivered or repledged by the Company as well as the fair value of financial instruments which could be further repledged by the receiving counterparty (in thousands):
		December 31,		December 31,
		2013		2012
	Collateral permitted to be delivered or repledged	$	1,315,803	$	50,717
	Collateral that was delivered or repledged	1,231,468		50,717
	Collateral permitted to be further repledged by the receiving counterparty	142,938		—
Financial Instruments Owned and Pledged to Counterparties that Do Not Have Right to Sell or Repledge	'
	The table below presents information about assets pledged by the Company (in thousands):
		December 31,		December 31,
		2013		2012
	Financial instruments owned, at fair value, pledged to counterparties that had the right to deliver or repledge	$	552,242	$	52,261
	Financial instruments owned, at fair value, pledged to counterparties that do not have the right to deliver or repledge	676,956		—

Receivable_from_and_Payable_to1

Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Tables)	12 Months Ended
	Dec. 31, 2013
Brokers and Dealers [Abstract]	'
Schedule of Amounts Receivable from and Payable to Brokers, Dealers and Clearing Organizations	'
	Amounts receivable from and payable to brokers, dealers and clearing organizations consist of the following (in thousands):
		December 31,		31-Dec-12
		2013
	Receivable:
	Clearing organizations and other	$	750,440	$	140,089
	Assets segregated or held in separate accounts under federal or other regulations	304,294		—
	Securities failed to deliver	202,517		2,880
	Total Receivable	$	1,257,251	$	142,969
	Payable:
	Clearing organizations and other	$	425,196	$	15,879
	Securities failed to receive	48,912		8,306
	Total Payable	$	474,108	$	24,185

Fixed_Assets_and_Leasehold_Imp1

Fixed Assets and Leasehold Improvements (Tables)	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Schedule of Fixed Assets and Leasehold Improvements	'
	Fixed assets and leasehold improvements comprise the following (in thousands):
		Depreciation	December 31,
		Period	2013			2012
	Computer hardware and software	3 years	$	223,141		$	178,187
	Leasehold improvements	*	115,046			60,750
	Telephone systems	5 years	3,848			—
	Furniture and fixtures	7 years	12,227			9,093
			354,262			248,030
	Less - Accumulated depreciation and amortization		(207,594		)	(164,689		)
			$	146,668		$	83,341
	______________________________
	*-Shorter of life of lease or useful life of assets

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2013
Investments [Abstract]	'
Summary of Investments	'
	Investments comprise strategic investments, including an investment in Knight prior to the Mergers and investment in the Deephaven Funds. Investments consist of the following (in thousands):
		December 31,		December 31,
		2013		2012
	Strategic investments:
	Investments accounted for under the equity method	$	82,234	$	—
	Investments held at fair value	3,925		202,672
	Common stock or equivalent of companies representing less than 20% equity ownership held at adjusted cost	33,813		45,766
	Total Strategic investments	119,972		248,438
	Deferred compensation investments	117		—
	Investment in Deephaven Funds	1,958		—
	Total Investments	$	122,047	$	248,438

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Summary of Goodwill	'
	The following table summarizes the Company’s Goodwill by segment (in thousands):
		December 31,				31-Dec-12
		2013
	Market Making	$	15,427			$	4,645
	Global Execution Services	832				—
	Total	$	16,259			$	4,645
Finite-Lived Intangible Assets, Net of Accumulated Amortization	'
	The following tables summarize the Company’s Intangible assets, net of accumulated amortization by segment and type (in thousands):
		December 31,				31-Dec-12
		2013
	Market Making
	Trading rights	$	48,920			$	48,903
	Technology	53,315				3,487
	Total	102,235				52,390
	Global Execution Services
	Customer relationships	33,278				—
	Trade names	3,800				—
	Technology	38,682				—
	Total	75,760				—
	Corporate and Other
	Technology	13,500				—
	Consolidated Total	$	191,495			$	52,390
			December 31,				31-Dec-12
			2013
	Customer relationships (1)	Gross carrying amount	$	35,000			$	—
		Accumulated amortization	(1,722		)		—
		Net carrying amount	33,278				—
	Trading rights (2)	Gross carrying amount	62,450				58,095
		Accumulated amortization	(13,530		)		(9,192		)
		Net carrying amount	48,920				48,903
	Trade names (3)	Gross carrying amount	4,000				—
		Accumulated amortization	(200		)		—
		Net carrying amount	3,800				—
	Technology (4)	Gross carrying amount	120,346				5,580
		Accumulated amortization	(14,849		)		(2,093		)
		Net carrying amount	105,497				3,487
	Total	Gross carrying amount	221,796				63,675
		Accumulated amortization	(30,301		)		(11,285		)
		Net carrying amount	$	191,495			$	52,390
	________________________________________
	(1)	Customer relationships relate to KCG Hotspot and KCG BondPoint. The weighted average remaining life is approximately 10 years as of December 31, 2013. Lives may be reduced depending upon actual retention rates.
	(2)	Trading rights provide the Company with the rights to trade on certain exchanges. The weighted average remaining life of trading rights with definite useful lives is approximately eight and nine years as of December 31, 2013 and December 31, 2012, respectively. As of December 31, 2013 and 2012, $7.6 million and $6.3 million, respectively, of trading rights have indefinite useful lives.
	(3)	Trade names relate to KCG Hotspot and KCG BondPoint. The weighted average remaining life is approximately ten years as of December 31, 2013.
	(4)	The weighted average remaining life for technology, including capitalized software, is approximately four and three years as of December 31, 2013 and December 31, 2012, respectively.
Summary of Amortization Expense Relating to Intangible Assets	'
	The following table summarizes the Company’s amortization expense from continuing operations relating to Intangible assets (in thousands):
		For the year ended December 31,
		2013				2012				2011
	Amortization expense	$	19,211			$	5,518			$	3,595
Summary of Estimated Amortization Expense for Future Years	'
	As of December 31, 2013, the following table summarizes the Company’s estimated amortization expense for future periods (in thousands):
		Amortization
		expense
	For the year ended December 31, 2014	$	33,542
	For the year ended December 31, 2015	32,617
	For the year ended December 31, 2016	31,527
	For the year ended December 31, 2017	30,396
	For the year ended December 31, 2018	19,396

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Summary of Long-Term Debt	'
	The carrying value and fair value of the Company's debt is as follows (in thousands):
		31-Dec-13				31-Dec-12
		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	Notes	$	—	$	—	$	15,000	$	15,000
	Cash Convertible Senior Subordinated Notes	117,259		118,432		—		—
	Senior Secured Notes	305,000		320,823		—		—
	First Lien Credit Facility	235,000		235,000		—		—
	Total Debt	$	657,259	$	674,255	$	15,000	$	15,000
Recorded Expenses with Respect to Long-Term Debt	'
	The Company recorded expenses with respect to the Debt as follows (in thousands):
		For the year ended December 31,
		2013		2012		2011
	Interest expense	$	34,138	$	1,194	$	164
	Amortization of debt issuance cost (1)	16,832		276		—
	Commitment fee (1)	792		1,034		—
	Total	$	51,762	$	2,504	$	164
	(1)	$3.6 million is included in Other expense

Related_Parties_Tables

Related Parties (Tables)	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Summary of Balances and Transactions with Related Parties or Their Affiliates	'
	As of the date and period indicated below, the Company had the following balances and transactions with the related parties or their affiliates as follows (in thousands):
	Statement of Operations	For the year ended
		December 31,
		2013
	Revenues
	Commissions and fees	$	2,583
	Trading revenues, net	437
	Interest, net	71
	Total revenues from related parties	$	3,091
	Expenses
	Execution and clearance fees	$	(5,706	)
	Interest expense	102
	Other expense	146
	Total expenses incurred with respect to related parties	$	(5,458	)
	Statement of Financial Condition	December 31,
		2013
	Assets
	Securities borrowed	$	57,732
	Receivable from brokers, dealers and clearing organizations	20,826
	Other assets	277
	Liabilities
	Securities loaned	$	116,062
	Payable to brokers, dealers and clearing organizations	17,820
	Accrued expenses and other liabilities	179

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2013
Share-based Compensation [Abstract]	'
Compensation Expense Relating to Restricted Awards	'
	The following is a summary of the changes in the incentive units for the year ended December 31, 2013 (units in thousands):
			Vested			Unvested
	Incentive units at January 1, 2013		24			45
	Issued		1			12
	Vested		53			(53	)
	Exercised		(28	)		—
	Canceled		(1	)		(4	)
	Incentive units at December 31, 2013		49			—
	The following is a schedule of the changes in GETCO's unvested Class E units (units in thousands):
			Units			Weighted Average Grant Price
	Unvested as of December 31, 2012		476			$	36.78
	Issued		—			—
	Vested		(442	)		37.24
	Forfeited		(34	)		30.89
	Unvested as of December 31, 2013		—
	The following is a schedule of the changes in GETCO's unvested Class B units (units in thousands):
			Units			Weighted Average Grant Price
	Unvested as of January 1, 2013		417			$	89.99
	Issued		58			73.54
	Vested		(438	)		87.86
	Forfeited		(37	)		89.28
	Unvested as of December 31, 2013		—
	Compensation expense from continuing operations relating to restricted awards, which is primarily recorded in Employee compensation and benefits, and the corresponding income tax benefit, which is recorded in Income tax (benefit) expense on the Consolidated Statements of Operations are presented in the following table (in thousands):
			For the year ended December 31,
			2013
	Stock award compensation expense		$	33,067
	Income tax benefit		11,573
Summary of Restricted Awards Activity	'
	The following table summarizes restricted awards activity for the six months ended December 31, 2013 (awards in thousands):
			Restricted Stock Units
			Number of			Weighted-
			Units			Average
						Grant date
						Fair Value
	1-Jul-13
	Conversion of outstanding Knight RSUs		3,251			$	11.22
	Granted		6,050			10.57
	Vested		(391	)		11.89
	Forfeited		(490	)		11.4
	Outstanding at December 31, 2013		8,420			$	10.71
Schedule of Weighted Average Assumption	'
	The weighted average assumptions used for stock options granted were as follows:
			2013
	Dividend yield		—	%
	Expected volatility		35	%
	Risk-free interest rate		1	%
	Expected life (in years)		3.5
Compensation Expense Relating to Stock Options	'
	Compensation expense from continuing operations relating to stock options and SARs, all of which was recorded in Employee compensation and benefits, as well as the corresponding income tax benefit, which is recorded in Income tax benefit on the Consolidated Statements of Operations are as follows (in thousands):
			For the year ended December 31,
			2013
	Stock option and SAR compensation expense		$	1,813
	Income tax benefit		635
Summary of Stock Option Activity	'
	The following table summarizes stock option and SAR activity and stock options exercisable for the six months ended December 31, 2013 (awards in thousands):
		Number of Stock Awards			Weighted-				Aggregate				Weighted-
					Average				Intrinsic				Average
					Exercise				Value				Remaining
					Price								Life (years)
	1-Jul-13	—			$	—
	Conversion of outstanding Knight options	782			41.25
	Granted at market value (1)	4,323			15.19
	Exercised	—			—
	Forfeited or expired	(138	)		45.32
	Outstanding at December 31, 2013 (1)	4,967			$	18.45			$	3,621			4.23
	Exercisable at December 31, 2013	644			$	40.37			$	—			2.23
	Available for future grants at December 31, 2013 *	19,160
	* Represents both options and awards available for grant.
	(1) Includes 1.7 million of SARs.
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range	'
			Options Outstanding									Options Exercisable
	Range of Exercise Prices		Outstanding			Weighted-		Weighted-				Number		Weighted-
			at 12/31/13			Average		Average				Exercisable		Average
						Remaining		Exercise				at 12/31/13		Exercise
						Contractual		Price						Price
						Life
	$8.24 - $8.24		833			4.61		$	8.24			—		$	—
	$8.25- $8.25		91			4.64		8.25				—		—
	$11.65 - $11.65		1,700			4.51		11.65				—		—
	$22.50 - $22.50		1,700			4.51		22.5				—		—
	$23.70 - $53.91		640			2.23		40.28				640		40.28
	$58.08 - $58.08		3			3.01		58.08				3		58.08
			4,967			4.23		$	18.45			643		$	40.37
Schedule of compensation costs	'
	Compensation expense (benefit) related to the Class B, Class E and Incentive units, all of which are recorded within Employee compensation and benefits on the Consolidated Statements of Operations are as follows (in thousands):
			For the year ended December 31,
			2013				2012				2011
	Class B and E units		$	19,860			$	12,320			$	40,466
	Incentive units		2,446				1,264				858
	Total		$	22,306			$	13,584			$	41,324

Employee_Benefit_Plan_Tables

Employee Benefit Plan (Tables)	12 Months Ended
	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]	'
Total Yearly Expenses of Employee Benefit Plan	'
	The total expense recognized with respect to the 401(k) Plan is included in Employee compensation and benefits on the Consolidated Statements of Operations, as follows (in thousands):
	For the year ended December 31, 2013	$	2,959

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Schedule of Components of Income Tax Expense (Benefit)	'
	The (benefit) provision for income taxes from continuing operations consists of (in thousands):
		For the years ended December 31,
		2013			2012			2011
	Current:
	U.S. federal	$	(194	)	$	(627	)	$	2,047
	U.S. state and local	2,902			618			1,218
	Non U.S.	3,773			8,708			29,910
		$	6,481		$	8,699		$	33,175
	Deferred:
	U.S. federal	$	(108,077	)	1,771			(949		)
	U.S. state and local	—			1,046			(263		)
	Non U.S.	(599		)	(1,240		)	(1,122		)
		$	(108,676	)	$	1,577		$	(2,334	)
	Provision (benefit) for income taxes	$	(102,195	)	$	10,276		$	30,841
Income tax rate reconciliation	'
	The following table reconciles the U.S. federal statutory income tax to the Company's actual income tax from continuing operations (in thousands):
		For the years ended December 31,
		2013			2012			2011
	U.S. federal statutory income tax (benefit) expense	$	6,235		$	9,249		$	67,739
	Income not subject to U.S. corporate income tax	(14,071		)	(7,095		)	(65,718		)
	U.S. state and local income taxes, net of U.S. federal income tax effect	1,886			772			478
	Deferred tax benefit resulting from the Company becoming subject to U.S. corporate income taxes	(103,499		)	—			—
	Nondeductible expenses (1)	3,627			200			133
	Foreign taxes	3,603			7,468			29,118
	Other, net	24			(318		)	(909		)
	Income tax (benefit) expense	$	(102,195	)	$	10,276		$	30,841
	(1) Nondeductible expenses include nondeductible compensation and meals and entertainment.
Schedule of Deferred Tax Assets and Liabilities	'
		For the years ended December 31,
		2013			2012
	Deferred tax assets:
	Employee compensation and benefit plans	$	16,629		$	527
	Fixed assets and other amortizable assets	90,130			3,742
	Reserves	4,362			—
	Valuation of investments	31,154			—
	Net operating loss carryforwards, net	125,728			1,041
	Less: Valuation allowance on net operating loss carryforwards	(36,043		)	—
	Total deferred tax assets	$	231,960		$	5,310
	Deferred tax liabilities
	Employee compensation and benefit plans	$	—		$	502
	Fixed assets and other amortizable assets	29,077			2,558
	Valuation of investments	10,414			1,831
	Reduction in foreign tax credit for Non-U.S. NOL carryforwards	18,885			—
	Total deferred tax liabilities	58,376			4,891
	Net deferred tax assets	$	173,584		$	419
Schedule of Unrecognized Tax Benefits Roll Forward	'
	The following table reconciles the beginning and ending amount of unrecognized tax benefits (in thousands):
		For the year ended December 31,
		2013
	Balance at beginning of period	$	—
	Increases based on tax positions related to prior periods (1)	1,464
	Decreases based on tax positions related to prior periods	—
	Decreases related to settlements with taxing authorities	—
	Balance at the end of the period	$	1,464
	(1) Increases relate to unrecognized tax benefits that inure to the Company as a result of the Mergers.

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2013
Equity [Abstract]	'
Accumulated Other Comprehensive Income (Loss)	'
	The following table presents changes in Accumulated other comprehensive income, net of tax by component for the years ended December 31, 2012 and 2013 (in thousands):
		Unrealized Gains (Losses) on Available-for-Sale Securities			Foreign Currency Translation Adjustments		Total
	Balance January 1, 2012	$	—		$	—	$	—
	Other comprehensive income (loss)	114,319			—		114,319
	Balance December 31, 2012	114,319			—		114,319
	Other comprehensive income (loss)	13,689			1,365		15,054
	Reclassification of gain on investment in Knight Common Stock(1)	(127,972		)	—		(127,972		)
	Net current-period other comprehensive loss	(114,283		)	1,365		(112,918		)
	Balance December 31, 2013	$	36		$	1,365	$	1,401
	(1) As a result of the Mergers, the Company recorded a non-cash gain of $128.0 million on its investment in Knight Common Stock, which it recognized within Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013 and reversed any previous unrealized gains out of Other comprehensive income.

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Schedule of Reconciliation of Earnings Per Share	'
	The following is a reconciliation of the numerators and denominators of the basic and diluted earnings per share computations from continuing operations for the years ended December 31, 2012 and 2011 (in thousands):
		For the year ended December 31,
		2013					2012				2011
		Numerator /			Denominator /		Numerator /		Denominator /		Numerator /		Denominator /
					shares		net		shares		net		shares
		net income					income				income
	Income from continuing operations and shares used in basic calculations	$	120,008		80,143		$	16,151	48,970		162,700		50,688
	Effect of dilutive stock based awards				872				—				—
	Income from continuing operations and shares used in diluted calculations	$	120,008		81,015		$	16,151	48,970		162,700		50,688
	(Loss) income from continuing operations allocated to preferred and participating units	$	(21,565	)			$	1,092			$	12,510
	Income from continuing operations attributable to common shareholders	$	141,573				$	15,059			$	150,190
	Basic earnings per common share from continuing operations				$	1.77			$	0.31			$	2.96
	Diluted earnings per common share from continuing operations				$	1.75			$	0.31			$	2.96

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Schedule of Lease and Contract Obligations	'
	The future minimum payments including interest under the capitalized leases at December 31, 2013 consist of (in thousands):
			Minimum Payments
	2014		8,222
	2015		2,072
	Total		$	10,294
Schedule of Interest Expense, Capital Lease	'
	The total interest expense related to capital leases for the years ended December 31, 2013, 2012 and 2011 included in the Consolidated Statements Operations is as follows (in thousands):
		For the year ended December 31,
		2013			2012		2011
	Interest expense - Capital leases	$	700		$	1,376	$	982
Schedule of Future Minimum Rental Payments for Operating Leases	'
	The Company leases certain computer and other equipment under noncancelable operating leases. As of December 31, 2013, future minimum rental commitments under all noncancelable office, computer and equipment leases (“Gross Lease Obligations”), and Sublease Income were as follows (in thousands):
		Gross Lease			Sublease		Net Lease
		Obligations			Income		Obligations
	Year ending December 31, 2014	$	29,689		$	4,315	$	25,374
	Year ending December 31, 2015	27,915			4,914		23,001
	Year ending December 31, 2016	27,571			4,850		22,721
	Year ending December 31, 2017	27,036			4,426		22,610
	Year ending December 31, 2018	26,492			2,720		23,772
	Thereafter through December 31, 2027	75,552			12,521		63,031
	Total	$	214,255		$	33,746	$	180,509

Net_capital_requirements_Table

Net capital requirements (Tables)	12 Months Ended
	Dec. 31, 2013
Brokers and Dealers [Abstract]	'
Net Capital Levels and Requirements for U.S. Registered Broker-Dealer Subsidiary	'
	The following table sets forth the net capital levels and requirements for the Company’s U.S. registered broker dealer subsidiaries at December 31, 2013 as filed in their respective regulatory filings (in thousands):
	Entity	Net Capital		Net Capital		Excess Net
				Requirement		Capital
	Knight Capital Americas LLC	$	396,655	$	22,300	$	374,355
	OCTEG, LLC	98,737		1,000		97,737
	GETCO Execution Services, LLC	11,433		250		11,183
Financial Resource Requirements on Significant Foreign Regulated Broker-Dealer	'
	The following table sets forth the financial resource requirement for the following significant foreign regulated broker dealers at December 31, 2013 (in thousands):
	Entity	Financial		Resource		Excess
		Resources		Requirement		Financial
						Resources
	GETCO Europe Limited	$	157,254	$	80,900	$	76,354
	KCG Europe Limited	97,892		65,967		31,927

Business_Segments_Tables

Business Segments (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Income (Loss) from Continuing Operations Before Income Taxes and Total Assets by Segment	'
	The Company’s revenues, income (loss) from continuing operations before income taxes (“Pre-tax earnings”) and total assets by segment are summarized in the following table (in thousands):
		Market		Global Execution Services			Corporate			Consolidated
		Making					and Other			Total
	For the year ended December 31, 2013:
	Revenues	$	688,197	$	197,766		$	134,208		$	1,020,171
	Pre-tax earnings	103,559		(25,739		)	(60,007		)	17,813
	Total assets	3,939,965		1,106,448			1,944,802			6,991,215
	For the year ended December 31, 2012:
	Revenues	$	495,427	$	36,211		$	19,596		$	551,234
	Pre-tax earnings	34,887		(7,330		)	(1,130		)	26,427
	Total assets	1,408,516		33,623			245,397			1,687,536
	For the year ended December 31, 2011:
	Revenues	$	862,760	$	27,599		$	25,089		$	915,448
	Pre-tax earnings	203,886		(15,406		)	5,061			193,541
	Total assets	1,191,724		19,928			90,703			1,302,355
	The Company operates in the U.S. and internationally, primarily in Europe and Asia. The following table presents Revenues by geographic area.
		U.S.		International			Consolidated
							Total
	For the year ended December 31, 2013:
	Revenues	$	827,245	$	192,926		$	1,020,171
	For the year ended December 31, 2012:
	Revenues	$	340,117	$	211,117		$	551,234
	For the year ended December 31, 2011:
	Revenues	$	489,514	$	425,934		$	915,448

Condensed_Financial_Statements1

Condensed Financial Statements of Knight Capital Group, Inc. (parent only) (Tables)	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Statements Of Financial Condition Parent Only	'
	Presented below are the Condensed Statements of Financial Condition, Operations and Cash Flows for the Company on an unconsolidated basis.
	Statements of Financial Condition
	KCG Holdings, Inc. (parent only)
		December 31,
		2013			2012
		(in thousands)
	Assets
	Cash and cash equivalents	$	253,017		$	114,511
	Financial instruments owned, at fair value	—			2
	Receivable from subsidiaries	60,460			216,266
	Investments in subsidiaries	1,356,412			773,818
	Goodwill and intangible assets, less accumulated amortization	—			8,132
	Income taxes receivable	90			—
	Deferred tax asset	144,109			—
	Subordinated loans to subsidiaries	250,000			—
	Other assets	21,182			1,039
	Total assets	$	2,085,270		$	1,113,768
	Liabilities & equity
	Liabilities
	Payable to subsidiaries	25,705			47,998
	Accrued expenses and other liabilities	12,313			84,959
	Debt	540,000			15,000
	Total liabilities	578,018			147,957
	Redeemable preferred member's equity	—			311,139
	Total equity	1,507,252			654,672
	Total liabilities & equity	$	2,085,270		$	1,113,768
Statements Of Operations Parent Only	'
	Statements of Operations
	KCG Holdings, Inc. (parent only)
		For the year ended December 31,
		2013			2012			2011
		(in thousands)
	Revenues
	Investment income and other, net	$	3,717		$	5,981		$	2,001
	Total revenues	3,717			5,981			2,001
	Expenses
	Employee compensation and benefits	31,970			(12,251		)	7,023
	Interest	28,476			1,195			256
	Depreciation and amortization	698			1,395			698
	Professional fees	30,488			4,997			1,484
	Bank fees	9,268			336			286
	Other	20,561			1,157			852
	Total expenses	121,461			(3,171		)	10,599
	(Loss) income before income taxes and equity in earnings of subsidiaries	(117,744		)	9,152			(8,598		)
	Income tax benefit	(120,761		)	—			—
	Income (loss) before equity in earnings of subsidiaries	3,017			9,152			(8,598		)
	Equity in earnings of subsidiaries	117,071			6,999			171,298
	Net income	$	120,088		$	16,151		$	162,700
Statements Of Cash Flows Parent Only	'
	Statements of Cash Flows
	KCG Holdings, Inc. (parent only)
		For the year ended December 31,
		2013			2012			2011
		(In thousands)
	Cash flows from operating activities
	Net income	$	120,088		$	16,151		$	162,700
	Adjustments to reconcile net income to net cash used in operating activities
	Equity in earnings of subsidiaries	(117,071		)	(6,999		)	(171,298		)
	Writedown and amortization of debt issuance costs	16,931			52			—
	Amortization of intangibles	698			1,395			698
	Decrease (increase) in operating assets
	Subordinated loan receivable	(250,000		)	—			—
	Receivable from subsidiaries	(67,523		)	(97,375		)	(89,814		)
	Deferred tax asset	(144,109		)	—			—
	Income taxes receivable	(90		)	—			—
	Other assets	(15,351		)	31,031			48,653
	(Decrease) increase in operating liabilities
	Payable to subsidiaries	(2,024		)	11,756			33,932
	Accrued expenses and other liabilities	59,921			5,106			718
	Net cash used in operating activities	(398,530		)	(38,883		)	(14,411		)
	Cash flows from investing activities
	Cash acquired upon acquisition of Knight Capital Group, Inc.	509,133			—			—
	Cash received from sale of Urban Financial of America, LLC	85,406			—			—
	Acquisition of Automat Limited	—			—			(10,975		)
	Dividends received from subsidiaries	646,425			161,606			127,530
	Capital contributions to subsidiaries	(238,909		)	(70,794		)	(84,928		)
	Net cash provided by investing activities	1,002,055			90,812			31,627
	Cash flows from financing activities
	Proceeds from issuance of Credit Agreement	535,000			—			—
	Partial repayment of Credit Agreement	(300,000		)	—			—
	Proceeds from issuance of Senior Secured Notes	305,000			—			—
	Proceeds from issuance of notes payable	—			—			15,000
	Repayment of notes payable	(15,000		)	—			—
	Payment of debt issuance costs	(34,952		)	—			—
	Issuance of equity to General Atlantic	55,000			—			—
	Payment to former Knight Capital Group, Inc. stockholders	(720,000		)	—			—
	Repayment of Knight Convertible Notes	(257,741		)	—			—
	Funding of collateral account for Knight Convertible Notes	(117,259		)	—			—
	Payment out of collateral account for Knight Convertible Notes	117,259			—			—
	Proceeds from stock issuance	—			12,320			41,365
	Member distributions	(21,002		)	(62,234		)	(124,791		)
	Cost of common stock repurchased	(11,324		)	—			—
	Net cash (used in) provided by financing activities	(465,019		)	(49,914		)	(68,426		)
	Increase in cash and cash equivalents	138,506			2,015			(51,210		)
	Cash and cash equivalents at beginning of period	114,511			112,496			163,706
	Cash and cash equivalents at end of period	$	253,017		$	114,511		$	112,496
	Supplemental disclosure of cash flow information:							—
	Cash paid for interest	$	26,239		$	1,116		$	92
	Cash paid for income taxes	$	365		$	—		$	—

Merger_of_GETCO_and_Knight_Det

Merger of GETCO and Knight (Detail) (USD $)	0 Months Ended	12 Months Ended
	Jul. 02, 2013	Dec. 31, 2013
Merger Transaction [Line Items]	'	'
Right of Knight shareholders to elect to receive per share value in cash under the agreement (in dollars per share)	$3.75	'
Shares granted to former shareholders (in shares)	41,900,000	'
Jefferies [Member]	'	'
Merger Transaction [Line Items]	'	'
Maximum cash entitled by shareholders to receive under the agreement	$720,000,000	'
GETCO [Member]	'	'
Merger Transaction [Line Items]	'	'
Number of shares to be received by GETCO members (in shares)	75,900,000	'
Number of warrants to acquire shares of common stock (in shares)	24,300,000	'
Shares outstanding (in shares)	116,800,000	'
Warrants one [Member]	'	'
Merger Transaction [Line Items]	'	'
Warrants receivable from holding company (in shares)	8,100,000	'
Exercise price of warrant (in dollars per share)	$12	'
Term of warrant	'4 years	'
Warrants two [Member]	'	'
Merger Transaction [Line Items]	'	'
Warrants receivable from holding company (in shares)	8,100,000	'
Exercise price of warrant (in dollars per share)	$13.50	'
Term of warrant	'5 years	'
Warrants three [Member]	'	'
Merger Transaction [Line Items]	'	'
Warrants receivable from holding company (in shares)	8,100,000	'
Exercise price of warrant (in dollars per share)	$15	'
Term of warrant	'6 years	'
Knight Class A Common Stock [Member]	'	'
Merger Transaction [Line Items]	'	'
Par Value (in dollars per share)	$0.01	'
KCG Class A Common Stock [Member]	'	'
Merger Transaction [Line Items]	'	'
Par Value (in dollars per share)	$0.01	'
Knight [Member]	'	'
Merger Transaction [Line Items]	'	'
Gain recognized	'	128,000,000
Total Purchase Price	1,373,134,000	'
Deferred tax asset, net	62,329,000	'
Merger costs	'	$38,900,000

Merger_of_GETCO_and_Knight_Ass

Merger of GETCO and Knight - Assets Acquired and Liabilities Assumed (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Jul. 02, 2013
In Thousands, unless otherwise specified			Knight [Member]
Identifiable Net Assets	'	'	'
Cash and cash equivalents	'	'	$509,133
Cash and securities segregated under federal and other regulations	'	'	203,045
Financial instruments owned	'	'	1,937,929
Securities borrowed	'	'	1,158,981
Receivable from brokers, dealers and clearing organizations	'	'	1,369,474
Fixed assets and leasehold improvements	'	'	80,280
Investments	'	'	106,353
Intangible assets	'	'	155,425
Assets within discontinued operations	'	'	5,607,063
Deferred tax asset, net	'	'	62,329
Other assets	'	'	141,617
Total Assets	'	'	11,331,629
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]	'	'	'
Financial instruments sold, not yet purchased	'	'	1,512,983
Collateralized financings	'	'	1,166,211
Payable to brokers, dealers and clearing organizations	'	'	635,914
Payable to customers	'	'	527,918
Accrued compensation expense	'	'	107,409
Accrued expenses and other liabilities	'	'	126,507
Liabilities within discontinued operations	'	'	5,518,168
Long-term debt	'	'	375,000
Total Liabilities	'	'	9,970,110
Total identified assets acquired, net of assumed liabilities	'	'	1,361,519
Goodwill	16,259	4,645	11,615
Total Purchase Price	'	'	$1,373,134

Merger_of_GETCO_and_Knight_Int

Merger of GETCO and Knight - Intangible Assets Acquired (Details) (USD $)	12 Months Ended			0 Months Ended		0 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Jul. 02, 2013	Jul. 02, 2013	Jul. 02, 2013	Jul. 02, 2013	Jul. 02, 2013		Jul. 02, 2013	Jul. 02, 2013
			Knight [Member]	Technology [Member]	Customer relationships [Member]	Trade names [Member]	Trading rights [Member]		Minimum [Member]	Maximum [Member]
				Knight [Member]	Knight [Member]	Knight [Member]	Knight [Member]		Customer relationships [Member]	Customer relationships [Member]
									Knight [Member]	Knight [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'		'	'
Intangible assets	'	'	$155,425	$110,504	$35,000	$4,000	$5,921	[1]	'	'
Goodwill	16,259	4,645	11,615	'	'	'	'		'	'
Total	'	'	$167,040	'	'	'	'		'	'
Weighted average useful life	'6 years	'9 years	'	'5 years	'	'10 years	'7 years		'9 years	'11 years
[1]	Trading rights include both assets with a finite useful life and assets with an indefinite useful life. The 7 years amortization period only applies to assets with a finite useful life.

Merger_of_GETCO_and_Knight_Pro

Merger of GETCO and Knight - Proforma Information (Details) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]	'	'	'
Revenues - Reported	$1,020,171	$551,234	$915,448
Net income from continuing operations - Reported	17,813	26,427	193,541
Net income - Reported	120,088	16,151	162,700
Diluted earnings (loss) per share from continuing operations (in dollars per share)	$1.75	$0.31	$2.96
Diluted earnings (loss) per share (in dollars per share)	$1.75	$0.31	$2.96
Knight [Member]	'	'	'
Business Acquisition [Line Items]	'	'	'
Revenues	486,119	'	'
Income from continuing operations, before income taxes	54,070	'	'
Revenues - Reported	1,020,171	551,234	'
Revenues - Pro Forma	1,421,566	1,020,334	'
Net income from continuing operations - Reported	120,008	16,151	'
Net income from continuing operations - Pro Forma	-69,414	-286,656	'
Net income - Reported	120,088	16,151	'
Net income - Pro Forma	($98,394)	($355,130)	'
Diluted earnings (loss) per share from continuing operations (in dollars per share)	$1.75	$0.31	'
Diluted earnings (loss) per share from continuing operations - Pro Forma (in dollars per share)	($0.86)	($5.85)	'
Diluted earnings (loss) per share (in dollars per share)	$1.75	$0.31	'
Diluted earnings (loss) per share - Pro Forma (in dollars per share)	($1.21)	($7.25)	'

Significant_Accounting_Policie3

Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]	'	'	'
Maximum maturity of short-term investments	'90 days	'	'
Investment Income [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Gain on investments	$128	'	'
Foreign currency transactions [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Investment gain (loss) and other, net	($4.10)	$0.20	($2.40)
Software [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Amortization period, in years	'3 years	'	'
Minimum [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Amortization period, in years	'3 years	'	'
Fixed assets, useful life	'3 years	'	'
Maximum [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Amortization period, in years	'12 years	'	'
Fixed assets, useful life	'7 years	'	'

Significant_Accounting_Policie4

Significant Accounting Policies - Schedule of Interest Income and Interest Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]	'	'	'
Interest Income	$10,187	$3,070	$1,131
Interest Expense	-10,724	-5,427	-2,342
Interest, net	($537)	($2,357)	($1,211)

Significant_Accounting_Policie5

Significant Accounting Policies - Net Trading Revenue Including Dividend Income and Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]	'	'	'
Dividend Income	$26,237	$2,253	$4,700
Dividend Expense	($21,630)	($1,599)	($1,512)

Discontinued_Operations_Income

Discontinued Operations - Income Disclosures (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Expenses:	'	'	'
Compensation	$349,192	$157,855	$241,753
Payments for order flow	35,711	2,964	3,299
Other	43,094	23,073	26,587
Total expenses	1,002,358	524,807	721,907
Income from discontinued operations, net of tax	80	0	0
Segment, Discontinued Operations [Member]	'	'	'
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'
Revenues	39,868	'	'
Expenses:	'	'	'
Compensation	14,068	'	'
Execution and clearance fees	5,038	'	'
Payments for order flow	9,885	'	'
Other	10,748	'	'
Total expenses	39,739	'	'
Pre-tax income from discontinued operations	129	'	'
Income tax expense	-49	'	'
Income from discontinued operations, net of tax	$80	'	'

Assets_Segregated_or_Held_in_S2

Assets Segregated or Held in Separate Accounts Under Federal or Other Regulations - (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Cash and Cash Equivalents [Abstract]	'
Cash and cash equivalents segregated under federal or other regulations	$183,083
Receivables from brokers, dealers and clearing organizations (1)	304,294	[1]
Total assets segregated or held in separate accounts under federal or other regulations	$487,377
[1]	Segregated assets included within Receivables from brokers, dealers and clearing organizations comprise cash and cash equivalents and U.S. government obligations primarily held as deposits with exchange clearing organizations.

Fair_Value_of_Financial_Instru2

Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	$2,721,839		$654,875
Total fair value of financial instrument assets	2,898,074		864,694
Financial instruments sold, not yet purchased, at fair value	2,165,500		512,553
Total fair value of financial instrument liabilities	2,165,500		512,553
Equities [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	2,298,785	[1]	378,933	[2]
Financial instruments sold, not yet purchased, at fair value	1,851,006	[1]	423,740	[2]
Listed equity options [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	339,798		92,305
Financial instruments sold, not yet purchased, at fair value	252,282		69,757
Corporate debt [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	43,203		68,765
Financial instruments sold, not yet purchased, at fair value	42,122		19,056
Securities on deposit with clearing organizations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Securities on deposit with clearing organizations	170,235	[3]	7,147
CME Group [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	3,925		3,040
Deferred compensation investments [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Deferred compensation investments	117	[4]	'
Knight Preferred Share [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	1,958	[4]	199,632
Loan inventory [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	'		114,872
U.S. government obligations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	40,053		'
Financial instruments sold, not yet purchased, at fair value	15,076		'
Foreign currency forward contracts [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments sold, not yet purchased, at fair value	5,014		'
Level 1 [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	2,721,839		654,875
Total fair value of financial instrument assets	2,895,999		864,694
Financial instruments sold, not yet purchased, at fair value	'		512,553
Total fair value of financial instrument liabilities	2,160,486		512,553
Level 1 [Member] | Equities [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	2,298,785	[1]	378,933	[2]
Financial instruments sold, not yet purchased, at fair value	1,851,006	[1]	423,740	[2]
Level 1 [Member] | Listed equity options [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	339,798		92,305
Financial instruments sold, not yet purchased, at fair value	252,282		69,757
Level 1 [Member] | Corporate debt [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	43,203		68,765
Financial instruments sold, not yet purchased, at fair value	42,122		19,056
Level 1 [Member] | Securities on deposit with clearing organizations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Securities on deposit with clearing organizations	170,235	[3]	7,147
Level 1 [Member] | CME Group [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	3,925		3,040
Level 1 [Member] | Deferred compensation investments [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Deferred compensation investments	0	[4]	'
Level 1 [Member] | Knight Preferred Share [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	0	[4]	199,632
Level 1 [Member] | Loan inventory [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	'		114,872
Level 1 [Member] | U.S. government obligations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	40,053		'
Financial instruments sold, not yet purchased, at fair value	15,076		'
Level 1 [Member] | Foreign currency forward contracts [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments sold, not yet purchased, at fair value	0		'
Level 2 [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		0
Total fair value of financial instrument assets	2,075		0
Financial instruments sold, not yet purchased, at fair value	'		0
Total fair value of financial instrument liabilities	5,014		0
Level 2 [Member] | Equities [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0	[1]	0	[2]
Financial instruments sold, not yet purchased, at fair value	0	[1]	0	[2]
Level 2 [Member] | Listed equity options [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		0
Financial instruments sold, not yet purchased, at fair value	0		0
Level 2 [Member] | Corporate debt [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		0
Financial instruments sold, not yet purchased, at fair value	0		0
Level 2 [Member] | Securities on deposit with clearing organizations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Securities on deposit with clearing organizations	0	[3]	0
Level 2 [Member] | CME Group [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	0		0
Level 2 [Member] | Deferred compensation investments [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Deferred compensation investments	117	[4]	'
Level 2 [Member] | Knight Preferred Share [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	1,958	[4]	0
Level 2 [Member] | Loan inventory [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	'		0
Level 2 [Member] | U.S. government obligations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		'
Financial instruments sold, not yet purchased, at fair value	0		'
Level 2 [Member] | Foreign currency forward contracts [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments sold, not yet purchased, at fair value	5,014		'
Level 3 [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		0
Total fair value of financial instrument assets	0		0
Financial instruments sold, not yet purchased, at fair value	'		0
Total fair value of financial instrument liabilities	0		0
Level 3 [Member] | Equities [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0	[1]	0	[2]
Financial instruments sold, not yet purchased, at fair value	0	[1]	0	[2]
Level 3 [Member] | Listed equity options [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		0
Financial instruments sold, not yet purchased, at fair value	0		0
Level 3 [Member] | Corporate debt [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		0
Financial instruments sold, not yet purchased, at fair value	0		0
Level 3 [Member] | Securities on deposit with clearing organizations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Securities on deposit with clearing organizations	0	[3]	0
Level 3 [Member] | CME Group [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	0		0
Level 3 [Member] | Deferred compensation investments [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Deferred compensation investments	0	[4]	'
Level 3 [Member] | Knight Preferred Share [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Total fair value of financial instrument assets	0	[4]	0
Level 3 [Member] | Loan inventory [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	'		0
Level 3 [Member] | U.S. government obligations [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments owned, at fair value	0		'
Financial instruments sold, not yet purchased, at fair value	0		'
Level 3 [Member] | Foreign currency forward contracts [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Financial instruments sold, not yet purchased, at fair value	$0		'
[1]	Equities of $697.9 million have been netted by their respective long and short positions by CUSIP number.
[2]	Equities of $5.9 million have been netted by their respective long and short positions by CUSIP number.
[3]	Securities on deposit with clearing organizations consist of U.S. government obligations and are recorded within Receivable from brokers, dealers and clearing organizations on the Consolidated Statements of Financial Condition.
[4]	Investment in CME Group, Deferred compensation investments and Investment in Deephaven Funds are included within Investments on the Consolidated Statements of Financial Condition.

Fair_Value_of_Financial_Instru3

Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) (Level 1 [Member], USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equities	$697.90	$5.90

Fair_Value_of_Financial_Instru4

Fair Value of Financial Instruments - Additional Information (Detail)	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
	USD ($)	GBP (£)	USD ($)
Fair Value Disclosures [Abstract]	'	'	'
Transfers of financial instruments between levels	$0	'	$0
Transfers of financial instruments between level 2 to level 1	0	'	0
Transfers of financial instruments out of level 3	0	'	0
Notional value of foreign currency forward	'	£ 80,000,000	'

Fair_Value_of_Financial_Instru5

Fair Value of Financial Instruments - Fair Value of Derivative Instruments in Consolidated Statements of Financial Condition and Effect of Changes in Fair Value on Consolidated Statements of Operations (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	$355,230		$93,615
Asset Contract	760,891		251,149
Liabilities Fair Value	269,078		72,363
Liabilities Contract	776,537		251,867
Receivables From/Payables to Brokers, Dealers and Clearing Organizations [Member] | Derivative instruments not designated as hedging instruments [Member] | Foreign Currency Futures contracts [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	89		8
Asset Contract	892		500
Liabilities Fair Value	142		5
Liabilities Contract	533		110
Receivables From/Payables to Brokers, Dealers and Clearing Organizations [Member] | Derivative instruments not designated as hedging instruments [Member] | Equity Future Contracts [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	223		270
Asset Contract	1,069		766
Liabilities Fair Value	1,089		477
Liabilities Contract	1,046		1,070
Receivables From/Payables to Brokers, Dealers and Clearing Organizations [Member] | Derivative instruments not designated as hedging instruments [Member] | Equity Swap [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	0		570
Asset Contract	0		1
Liabilities Fair Value	18		0
Liabilities Contract	1		0
Receivables From/Payables to Brokers, Dealers and Clearing Organizations [Member] | Derivative instruments not designated as hedging instruments [Member] | Fixed Income Futures Contracts [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	4,815		449
Asset Contract	18,280		49,498
Liabilities Fair Value	2,259		2,014
Liabilities Contract	15,202		53,882
Receivables From/Payables to Brokers, Dealers and Clearing Organizations [Member] | Derivative instruments not designated as hedging instruments [Member] | Commodity Contract [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	3,392		13
Asset Contract	10,629		1,060
Liabilities Fair Value	1,773		0
Liabilities Contract	3,806		0
Financial Instruments Owned, at Fair Value [Member] | Derivative instruments not designated as hedging instruments [Member] | Listed equity options [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	339,798		92,305
Asset Contract	730,020		199,324
Liabilities Fair Value	252,282		69,757
Liabilities Contract	755,947		196,804
Financial Instruments Owned, at Fair Value [Member] | Derivative instruments designated as hedging instruments [Member] | Foreign currency forward contracts [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	6,913	[1]	'
Asset Contract	1	[1]	'
Liabilities Fair Value	11,515	[1]	'
Liabilities Contract	2	[1]	'
Accrued Expenses and Other Liabilties [Member] | Derivative instruments not designated as hedging instruments [Member] | Foreign currency forward contracts [Member]	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Asset Fair Value	'		0
Asset Contract	'		0
Liabilities Fair Value	'		110
Liabilities Contract	'		$1
[1]	Designated as hedging instrument

Fair_Value_of_Financial_Instru6

Fair Value of Financial Instruments - Fair Value of Derivative Instruments Gain Loss Recognized (Detail) (Trading Revenues, Net [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivative instruments not designated as hedging instruments [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	$253,761		$272,235		$485,926
Derivative instruments not designated as hedging instruments [Member] | Foreign currency forward contracts [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	12,191		19,699		25,808
Derivative instruments not designated as hedging instruments [Member] | Equity Future Contracts [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	50,073		76,089		156,537
Derivative instruments not designated as hedging instruments [Member] | Equity Swap [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	11,736		8,116		18,624
Derivative instruments not designated as hedging instruments [Member] | Stock Option [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	37,035	[1]	50,446	[1]	90,389	[1]
Derivative instruments not designated as hedging instruments [Member] | Fixed Income Futures Contracts [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	80,511		81,933		170,414
Derivative instruments not designated as hedging instruments [Member] | Commodity Contract [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Derivative instruments not designated as hedging instruments, Gain (Loss)	62,215		35,952		24,154
Derivative instruments designated as hedging instruments [Member] | Foreign currency forward contracts [Member]	'		'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'
Accumulated other comprehensive income (loss)	($3,298)		$0		$0
[1]	Realized gains and losses on listed equity options relate to the Company’s market making activities in such options. Such market making activities also comprise trading in the underlying equity securities with gains and losses on such securities generally offsetting the gains and losses reported in this table. Gains and losses on such equity securities are also included in Trading revenue, net on the Company’s Consolidated Statements of Operations.

Fair_Value_of_Financial_Instru7

Fair Value of Financial Instruments - Fair Value of Gross amounts offset (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized, Asset	$1,736,983		$145,306
Gross Amounts Offset in the Statements of Financial Condition, Assets	10,870		462
Net Amounts of Assets Presented in the Statements of Financial Condition, Assets	1,726,113		144,844
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	1,350,469		50,717
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets	0		0
Net Amount, Assets	375,644		94,127
Gross Amounts of Recognized Derivatives, Liability	1,643,258		72,254
Gross Amounts of Recognized Derivatives, Liability	11,764		2,497
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	1,631,494		69,757
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	1,367,896		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	10,924		1,393
Net Amount, Liability	252,674		68,364
Listed equity options [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized, Asset	339,798		92,305
Gross Amounts Offset in the Statements of Financial Condition, Assets	0		0
Net Amounts of Assets Presented in the Statements of Financial Condition, Assets	339,798		92,305
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	0		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets	0		0
Net Amount, Assets	339,798		92,305
Gross Amounts of Recognized Derivatives, Liability	252,282		69,757
Gross Amounts of Recognized Derivatives, Liability	0		0
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	252,282		69,757
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	0		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	10,924		1,393
Net Amount, Liability	241,358		68,364
Securities borrowed [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized, Asset	1,357,387		52,261
Gross Amounts Offset in the Statements of Financial Condition, Assets	0		0
Net Amounts of Assets Presented in the Statements of Financial Condition, Assets	1,357,387		52,261
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	1,326,220		50,717
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets	0		0
Net Amount, Assets	31,167		1,544
Receivable from brokers, dealers and clearing organizations [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized, Asset	24,366	[1]	'
Gross Amounts Offset in the Statements of Financial Condition, Assets	0	[1]	'
Net Amounts of Assets Presented in the Statements of Financial Condition, Assets	24,366	[1]	'
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	24,249	[1]	'
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets	0	[1]	'
Net Amount, Assets	117	[1]	'
Futures [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized, Asset	8,519		740
Gross Amounts Offset in the Statements of Financial Condition, Assets	4,369		462
Net Amounts of Assets Presented in the Statements of Financial Condition, Assets	4,150		278
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	0		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets	0		0
Net Amount, Assets	4,150		278
Gross Amounts of Recognized Derivatives, Liability	5,263		2,497
Gross Amounts of Recognized Derivatives, Liability	5,263		2,497
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	0		0
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	0		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	0		0
Net Amount, Liability	0		0
Securities loaned [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized Derivatives, Liability	733,230		'
Gross Amounts of Recognized Derivatives, Liability	0		'
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	733,230		'
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	726,948		'
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	0		'
Net Amount, Liability	6,282		'
Financial instruments sold under agreements to repurchase [Member}	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized Derivatives, Liability	640,950		'
Gross Amounts of Recognized Derivatives, Liability	0		'
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	640,950		'
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	640,948		'
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	0		'
Net Amount, Liability	2		'
Foreign currency forward contracts [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized, Asset	6,913		'
Gross Amounts Offset in the Statements of Financial Condition, Assets	6,501		'
Net Amounts of Assets Presented in the Statements of Financial Condition, Assets	412		'
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	0		'
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets	0		'
Net Amount, Assets	412		'
Gross Amounts of Recognized Derivatives, Liability	11,515		'
Gross Amounts of Recognized Derivatives, Liability	6,501		'
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	5,014		'
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	0		'
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	0		'
Net Amount, Liability	5,014		'
Swaps [Member]	'		'
Offsetting Liabilities [Line Items]	'		'
Gross Amounts of Recognized Derivatives, Liability	18		'
Gross Amounts of Recognized Derivatives, Liability	0		'
Net Amounts of Assets Presented in the Statements of Financial Condition, Liability	18		'
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Liability	0		'
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Liability	0		'
Net Amount, Liability	$18		'
[1]	Represent reverse repurchase agreements at broker dealer

Collateralized_Transactions_Fi

Collateralized Transactions - Financial Instruments at Fair Value Received as Collateral that were Permitted to be Delivered or Repledged (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Securities Financing Transaction [Line Items]	'	'
Collateral permitted to be delivered or repledged	$552,242	$52,261
Fair value of financial instruments received as collateral [Member]	'	'
Securities Financing Transaction [Line Items]	'	'
Collateral permitted to be delivered or repledged	1,315,803	50,717
Collateral that was delivered or repledged	1,231,468	50,717
Collateral permitted to be further repledged by the receiving counterparty	$142,938	$0

Collateralized_Transaction_Add

Collateralized Transaction - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013
Collateralized Agreements [Abstract]	'
Repurchase agreements and other secured financings, maturity (years)	'1 year

Collateralized_Transactions_Fi1

Collateralized Transactions - Financial Instruments Owned and Pledged to Counterparties that Do Not Have Right to Sell or Repledge (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Collateralized Agreements [Abstract]	'	'
Collateral permitted to be delivered or repledged	$552,242	$52,261
Financial instruments owned, at fair value, pledged to counterparties that do not have the right to deliver or repledge	$676,956	$0

Receivable_from_and_Payable_to2

Receivable from and Payable to Brokers, Dealers, and Clearing Organizations - Schedule of Amounts Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Receivable/Payable:	'	'
Clearing organizations and other	$750,440	$140,089
Assets segregated or held in separate accounts under federal or other regulations	304,294	0
Securities failed to deliver	202,517	2,880
Total Receivable	1,257,251	142,969
Clearing organizations and other, Payable	425,196	15,879
Securities failed to receive, Payable	48,912	8,306
Total Payable	$474,108	$24,185

Fixed_Assets_and_Leasehold_Imp2

Fixed Assets and Leasehold Improvements - Schedule of Fixed Assets and Leasehold Improvements (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]	'	'
Fixed assets and leasehold improvements, gross	$354,262	$248,030
Less-Accumulated depreciation and amortization	-207,594	-164,689
Fixed assets and leasehold improvements, at cost, less accumulated depreciation and amortization	146,668	83,341
Computer hardware and software [Member]	'	'
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]	'	'
Depreciation Period	'3 years	'
Fixed assets and leasehold improvements, gross	223,141	178,187
Leasehold improvements [Member]	'	'
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]	'	'
Fixed assets and leasehold improvements, gross	115,046	60,750
Telephone systems [Member]	'	'
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]	'	'
Depreciation Period	'5 years	'
Fixed assets and leasehold improvements, gross	3,848	0
Furniture and fixtures [Member]	'	'
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]	'	'
Depreciation Period	'7 years	'
Fixed assets and leasehold improvements, gross	$12,227	$9,093

Investments_Details

Investments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013
			Investment Income [Member]
Schedule of Equity Method Investments [Line Items]	'	'	'
Investments accounted for under the equity method	$82,234,000	$0	'
Investments held at fair value	3,925,000	202,672,000	'
Common stock or equivalent of companies representing less than 20% equity ownership held at adjusted cost	33,813,000	45,766,000	'
Total Strategic investments	119,972,000	248,438,000	'
Deferred compensation investments	117,000	0	'
Investment in Deephaven Funds	1,958,000	0	'
Total Investments	122,047,000	248,438,000	'
Percentage of equity in common stock of private companies cover under strategic investment	20.00%	20.00%	'
Gain on investments	'	'	$128,000,000

Goodwill_and_Intangible_Assets2

Goodwill and Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Jul. 02, 2013
			Minimum [Member]	Maximum [Member]	Knight [Member]
Finite-Lived Intangible Assets [Line Items]	'	'	'	'	'
Amount	'	'	'	'	$155,425
Goodwill	$16,259	$4,645	'	'	$11,615
Amortization period, in years	'	'	'3 years	'12 years	'
Weighted average useful life	'6 years	'9 years	'	'	'

Goodwill_and_Intangible_Assets3

Goodwill and Intangible Assets - Summary of Goodwill (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Goodwill [Line Items]	'	'
Goodwill	$16,259	$4,645
Market Making [Member]	'	'
Goodwill [Line Items]	'	'
Goodwill	15,427	4,645
Global Execution Services [Member]	'	'
Goodwill [Line Items]	'	'
Goodwill	$832	$0

Goodwill_and_Intangible_Assets4

Goodwill and Intangible Assets - Finite-Lived Intangible Assets, Net of Accumulated Amortization (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Goodwill [Line Items]	'		'
Gross carrying amount	$221,796		$63,675
Accumulated amortization	-30,301		-11,285
Net carrying amount	191,495		52,390
Market Making [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	102,235		52,390
Electronic Execution Services [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	75,760		0
Trading rights [Member]	'		'
Goodwill [Line Items]	'		'
Gross carrying amount	62,450	[1]	58,095	[1]
Accumulated amortization	-13,530	[1]	-9,192	[1]
Net carrying amount	48,920	[1]	48,903	[1]
Trading rights [Member] | Market Making [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	48,920		48,903
Technology [Member]	'		'
Goodwill [Line Items]	'		'
Gross carrying amount	120,346	[2]	5,580	[2]
Accumulated amortization	-14,849	[2]	-2,093	[2]
Net carrying amount	105,497	[2]	3,487	[2]
Technology [Member] | Market Making [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	53,315		3,487
Technology [Member] | Electronic Execution Services [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	38,682		0
Technology [Member] | Corporate and Other [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	13,500		0
Customer and broker relationships [Member]	'		'
Goodwill [Line Items]	'		'
Gross carrying amount	35,000	[3]	0	[3]
Accumulated amortization	-1,722	[3]	0	[3]
Net carrying amount	33,278	[3]	0	[3]
Customer and broker relationships [Member] | Electronic Execution Services [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	33,278		0
Trade names [Member]	'		'
Goodwill [Line Items]	'		'
Gross carrying amount	4,000	[4]	0	[4]
Accumulated amortization	-200	[4]	0	[4]
Net carrying amount	3,800	[4]	0	[4]
Trade names [Member] | Electronic Execution Services [Member]	'		'
Goodwill [Line Items]	'		'
Net carrying amount	$3,800		$0
[1]	Trading rights provide the Company with the rights to trade on certain exchanges. The weighted average remaining life of trading rights with definite useful lives is approximately eight and nine years as of December 31, 2013 and December 31, 2012, respectively.
[2]	The weighted average remaining life for technology, including capitalized software, is approximately four and three years as of December 31, 2013 and December 31, 2012, respectively.
[3]	Customer relationships relate to KCG Hotspot and KCG BondPoint. The weighted average remaining life is approximately 10 years as of December 31, 2013. Lives may be reduced depending upon actual retention rates.
[4]	Trade names relate to KCG Hotspot and KCG BondPoint. The weighted average remaining life is approximately ten years as of December 31, 2013.

Goodwill_and_Intangible_Assets5

Goodwill and Intangible Assets - Finite-Lived Intangible Assets, Net of Accumulated Amortization (Parenthetical) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Customer and broker relationships [Member]	'	'
Goodwill [Line Items]	'	'
Amortization period, in years	'10 years	'
Trading rights [Member]	'	'
Goodwill [Line Items]	'	'
Amortization period, in years	'8 years	'9 years
Indefinite-lived intangible assets	$7.60	$6.30
Technology [Member]	'	'
Goodwill [Line Items]	'	'
Amortization period, in years	'4 years	'3 years
Trade names [Member]	'	'
Goodwill [Line Items]	'	'
Amortization period, in years	'10 years	'

Goodwill_and_Intangible_Assets6

Goodwill and Intangible Assets - Summary of Amortization Expense Relating to Intangible Assets (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Goodwill and Intangible Assets Disclosure [Abstract]	'	'	'
Amortization expense	$19,211	$5,518	$3,595

Goodwill_and_Intangible_Assets7

Goodwill and Intangible Assets - Summary of Estimated Amortization Expense for Future Years (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]	'
For the year ended December 31, 2014	$33,542
For the year ended December 31, 2015	32,617
For the year ended December 31, 2016	31,527
For the year ended December 31, 2017	30,396
For the year ended December 31, 2018	$19,396

Debt_Summary_of_LongTerm_Debt_

Debt - Summary of Long-Term Debt (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Debt Disclosure [Abstract]	'	'
Notes, Carrying Value	$0	$15,000
Notes, Fair Value	0	15,000
Convertible Notes, Carrying Amount	117,259	0
Convertible Notes, Fair Value	118,432	0
Senior Secured Notes, Carrying Value	305,000	0
Senior Secured Notes, Fair Value	320,823	0
Credit Agreement, Carrying Value	235,000	0
Credit Agreement, Fair Value	235,000	0
Long term debt	657,259	15,000
Total Long-term debt, Fair Value	$674,255	$15,000

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)

0 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

12 Months Ended

1 Months Ended

1 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

2 Months Ended

0 Months Ended

7 Months Ended

12 Months Ended

Aug. 05, 2013

Jul. 31, 2013

Mar. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2013

Jul. 31, 2013

Oct. 31, 2011

Jun. 30, 2013

Dec. 31, 2013

Jun. 05, 2013

Dec. 31, 2013

Jul. 02, 2013

Oct. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Oct. 23, 2013

Jul. 02, 2013

Jul. 02, 2013

Jul. 31, 2013

Dec. 31, 2013

Jul. 02, 2013

Jul. 31, 2013

Jul. 02, 2013

Jul. 02, 2013

Jul. 31, 2013

Jul. 02, 2013

Dec. 31, 2013

Dec. 31, 2013

Jul. 31, 2013

Jul. 02, 2013

Mar. 03, 2014

Oct. 23, 2013

Jan. 22, 2014

Jan. 22, 2014

Dec. 31, 2013

Notes Payable to Banks [Member]

Notes Payable to Banks [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Swingline Facilty [Member]

Swingline Facilty [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

LIBOR Floor [Member]

Prime Rate [Member]

Prime Rate [Member]

Borrowing Base A [Member]

Borrowing Base B Loan [Member]

LIBOR [Member]

LIBOR [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Other Expense [Member]

OCTEG-KCA [Member]

OCTEG-KCA [Member]

OCTEG-KCA [Member]

OCTEG-KCA [Member]

OCTEG-KCA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

OCTEG-KCA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

OCTEG-KCA [Member]

OCTEG-KCA [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

OCTEG-KCA [Member]

OCTEG-KCA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

Jefferies Finance LLC and Goldman Sachs Bank USA [Member]

OCTEG-KCA [Member]

Line of Credit Facility [Line Items]

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Debt amount

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$15,000,000

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Interest rate

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5.95%

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8.25%

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Early repayment fee

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3,000,000

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Issue of cash convertible senior subordinated notes

'

'

375,000,000

'

'

'

375,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash convertible senior subordinated notes due date

'

'

15-Mar-15

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Notes bear interest rate per year

'

'

'

3.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Date of commencing of notes

'

'

'

15-Sep-10

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Date of mature of notes

'

'

'

15-Mar-15

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deposit cash made to credit facility to repurchase convertible notes

'

375,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repayment of Knight Convertible Notes

257,700,000

'

'

257,741,000

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest payable

3,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Term credit agreement

'

'

'

235,000,000

0

'

'

'

'

'

'

305,000,000

'

'

'

'

'

'

'

'

'

'

535,000,000

'

450,000,000

'

'

'

'

'

'

'

'

'

'

'

'

Escrow agent fees and expenses

'

'

'

'

'

'

'

'

'

3,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of days to issue securities

'

'

'

'

'

'

'

'

'

'

'365 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional interest percent obligation from guarantor if certain obligations are not met

'

'

'

'

'

'

'

'

'

'

1.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount of consenting shareholders percentage of total debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

99.70%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Prepayment period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'60 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Early principal payments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000,000

300,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100,000,000

100,000,000

400,000,000

'

Write off of deferred debt issuance cost

'

'

'

16,832,000

[1]

276,000

[1]

0

[1]

'

'

'

'

'

'

'

'

'

13,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4,200,000

'

'

'

13,200,000

Cash held in collateral account

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

117,300,000

117,300,000

117,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving credit facility amount

'

'

'

'

'

'

'

'

'

'

'

'

'

50,000,000

'

'

'

'

50,000,000

750,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount outstanding

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

135,000,000

135,000,000

'

increase in line of credit facility, maximum borrowing capacity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate of credit agreement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.25%

'

2.25%

'

'

'

1.00%

'

'

'

'

'

Percentage points added to interest rate base

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.50%

'

'

'

'

'

0.50%

'

1.75%

2.25%

3.50%

'

'

'

'

'

'

Interest rate at end of period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.75%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal payments in 2014

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

235,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Periodic principal payment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Commitment fee percentage of average daily amount unused portion of revolving credit agreement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.35%

'

'

'

'

'

'

'

'

'

'

'

'

'

Prepayment premium percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loan guarantee percent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt issuance costs incurred

'

'

'

'

'

'

'

'

'

'

$37,400,000

'

$1,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Effective interest rate

'

'

'

'

'

'

'

'

'

'

9.00%

'

'

'

'

'

'

'

'

'

'

8.30%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

included in Other expense

Debt_Recorded_Expenses_with_Re

Debt - Recorded Expenses with Respect to Long-Term Debt (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Debt Disclosure [Abstract]	'		'		'
Interest expense	$34,138		$1,194		$164
Amortization of debt issuance cost	16,832	[1]	276	[1]	0	[1]
Commitment fee	792	[1]	1,034	[1]	0	[1]
Total	$51,762		$2,504		$164
[1]	included in Other expense

Related_Parties_Summary_of_Bal

Related Parties - Summary of Balances and Transactions with Related Parties or Their Affiliates (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	Party
Related Party Transaction [Line Items]	'	'	'
Number of related parties	2	'	'
Revenues	'	'	'
Commissions and fees	$275,474,000	$105,518,000	$284,620,000
Trading revenues, net	628,304,000	421,063,000	611,845,000
Expenses	'	'	'
Execution and clearance fees	246,414,000	185,790,000	289,025,000
Other expense	43,094,000	23,073,000	26,587,000
Assets	'	'	'
Securities borrowed	1,357,387,000	52,261,000	'
Receivable from brokers, dealers and clearing organizations	1,257,251,000	142,969,000	'
Other assets	147,322,000	16,806,000	'
Liabilities	'	'	'
Securities loaned	733,230,000	0	'
Payable to brokers, dealers and clearing organizations	474,108,000	24,185,000	'
Related Party [Member]	'	'	'
Liabilities	'	'	'
Advisory fees	49,800,000	'	'
Affiliated entity [Member]	'	'	'
Revenues	'	'	'
Commissions and fees	2,583,000	'	'
Trading revenues, net	437,000	'	'
Interest, net	71,000	'	'
Total revenues from related parties	3,091,000	'	'
Expenses	'	'	'
Execution and clearance fees	-5,706,000	'	'
Interest expense	102,000	'	'
Other expense	146,000	'	'
Total expenses incurred with respect to related parties	-5,458,000	'	'
Assets	'	'	'
Securities borrowed	57,732,000	'	'
Receivable from brokers, dealers and clearing organizations	20,826,000	'	'
Other assets	277,000	'	'
Liabilities	'	'	'
Securities loaned	116,062,000	'	'
Payable to brokers, dealers and clearing organizations	17,820,000	'	'
Accrued expenses and other liabilities	$179,000	'	'

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended						12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 19, 2013	Jul. 02, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013
			Stock Appreciation Rights (SARs) [Member]	Class B Units [Member]	Class E Units [Member]	KCG Plan [Member]	KCG Plan [Member]	Restricted Stock [Member]	Stock Options [Member]	Minimum [Member]	Maximum [Member]
										Stock Options [Member]	Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Expiration period	'	'	'	'	'	'	'	'	'	'5 years	'10 years
Number of shares authorized for grant (in shares)	'	'	'	'	'	32,700,000	20,700,000	'	'	'	'
Vesting period	'	'	'	'3 years	'3 years	'	'	'3 years	'3 years	'	'
Percent of shares vesting over vesting period	'	'	'	3.33%	3.33%	'	'	'	'	'	'
Unamortized compensation related to restricted awards outstanding	'	'	'	'	'	'	'	$67.30	'	'	'
Cost of unvested awards expected to be recognized over a weighted average life, years	'	'	'	'	'	'	'	'2 years 2 months	'	'	'
Weighted average fair value (USD per share)	'	'	'	'	'	'	'	'	$3.15	'	'
Unamortized compensation costs	1.3	'	7	9.4	'	'	'	'	'	'	'
Award expiration period	'	'	'1 year 10 months 12 days	'	'5 years	'	'	'	'	'	'
Number of Stock Awards, Exercised (in shares)	0	0	'	'	'	'	'	'	'	'	'
Employee compensation and benefit plans	3.8	3.5	'	'	'	'	'	'	'	'	'
Accelerated amortization	'	'	'	'	$3.50	'	'	'	'	'	'

StockBased_Compensation_Compen

Stock-Based Compensation - Compensation Expense Relating to Restricted Awards (Detail) (Restricted Stock [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Restricted Stock [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Stock award compensation expense	$33,067
Income tax benefit	$11,573

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Restricted Awards Activity (Detail) (Restricted Stock Units [Member], USD $)	6 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013
Restricted Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'
Number of Shares, Beginning Balance (in shares)	'
Number of Shares, Converted (in shares)	3,251
Number of Shares, Granted (in shares)	6,050
Number of Shares, Vested (in shares)	-391
Number of Shares, Forfeited (in shares)	-490
Number of Shares, Ending Balance (in shares)	8,420
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]	'
Weighted-Average Grant date Fair Value, Beginning Balance (in dollars per share)	'
Weighted Average Grant Date Fair Value, Number of Shares, Converted (in dollars per share)	$11.22
Weighted-Average Grant date Fair Value, Granted (in dollars per share)	$10.57
Weighted-Average Grant date Fair Value, Vested (in dollars per share)	$11.89
Weighted-Average Grant date Fair Value, Forfeited (in dollars per share)	$11.40
Weighted-Average Grant date Fair Value, Ending Balance (in dollars per share)	$10.71

Share_Based_Compensation_Weigh

Share Based Compensation - Weighted Average Assumptions Used For Stock Options (Details) (Stock Options [Member])	12 Months Ended
	Dec. 31, 2013
Stock Options [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Dividend yield	0.00%
Expected volatility	35.00%
Risk-free interest rate	1.00%
Expected life (in years)	'3 years 6 months

StockBased_Compensation_Compen1

Stock-Based Compensation - Compensation Expense Relating to Stock Options (Detail) (Stock Options [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Stock Options [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Stock option and SAR compensation expense	$1,813
Income tax benefit	$635

StockBased_Compensation_Summar1

Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $)	6 Months Ended		12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'		'
Number of Stock Awards, Beginning Balance (in shares)	0		'
Number of Stock Awards, Conversion Outstanding to options (in shares)	782,000		'
Number of Stock Awards, Granted at market value (in shares)	4,323,000		'
Number of Stock Options, Exercised (in shares)	0		0
Number of Stock Awards, Forfeited or expired (in shares)	-138,000		'
Number of Stock Options, Ending Balance (in shares)	4,967,000	[1]	'
Number of Stock Awards, Exercisable (in shares)	644,000		'
Available for future grants (in shares)	19,160,000	[2]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Weighted-Average Exercise Price, Beginning Balance (in dollars per share)	$0		'
Weighted-Average Exercise Price, Granted at Market Value (in dollars per share)	$41.25		'
Weighted-Average Exercise Price, Granted at market value (in dollars per share)	$15.19		'
Weighted-Average Exercise Price, Exercised (in dollars per share)	$0		'
Weighted-Average Exercise Price, Forfeited or expired (in dollars per share)	$45.32		'
Weighted-Average Exercise Price, Ending Balance (in dollars per share)	$18.45		'
Weighted-Average Exercise Price, Exercisable	$40.37		'
Aggregate Intrinsic Value of Options, Outstanding	$3,621		'
Aggregate Intrinsic Value of Options, Exercised	$0		'
Weighted-Average Remaining Life, Outstanding	'4 years 2 months 23 days		'
Weighted-Average Remaining Life, Exercisable	'2 years 2 months 23 days		'
Options Outstanding (in shares)	4,967,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'4 years 2 months 23 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$18.45		'
Options Exercisable (in shares)	643,000		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$40.37		'
Stock Appreciation Rights (SARs) [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'		'
Number of Stock Awards, Granted at market value (in shares)	1,700,000		'
$8.24 - $8.24 [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Options Outstanding (in shares)	833,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'4 years 7 months 10 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$8.24		'
Options Exercisable (in shares)	0		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$0		'
$8.25- $8.25 [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Options Outstanding (in shares)	91,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'4 years 7 months 21 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$8.25		'
Options Exercisable (in shares)	0		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$0		'
$11.65 - $11.65 [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Options Outstanding (in shares)	1,700,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'4 years 6 months 4 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$11.65		'
Options Exercisable (in shares)	0		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$0		'
$22.50 - $22.50 [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Options Outstanding (in shares)	1,700,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'4 years 6 months 4 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$22.50		'
Options Exercisable (in shares)	0		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$0		'
$23.70 - $53.91 [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Options Outstanding (in shares)	640,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'2 years 2 months 23 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$40.28		'
Options Exercisable (in shares)	640,000		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$40.28		'
$58.08 - $58.08 [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'		'
Options Outstanding (in shares)	3,000		'
Options Outstanding, Weighted Average Remaining Contractual Life	'3 years 0 months 4 days		'
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$58.08		'
Options Exercisable (in shares)	3,000		'
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$58.08		'
[1]	Includes 1.7 million of SARs.
[2]	Represents both options and awards available for grant.

StockBased_Compensation_Incent

Stock-Based Compensation - Incentive Units (Details) (Incentive Units [Member], Common Class A [Member])	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Incentive Units [Member] | Common Class A [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]	'
Beginning balance (in shares)	24
Issued (in shares)	1
Number of Shares, Vested (in shares)	-53
Exercised (in shares)	-28
Canceled (in shares)	-1
Ending balance (in shares)	49
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'
Number of Shares, Beginning Balance (in shares)	45
Number of Shares, Granted (in shares)	12
Number of Shares, Forfeited (in shares)	-4
Number of Shares, Ending Balance (in shares)	0

StockBased_Compensation_Class_

Stock-Based Compensation - Class B Units (Details) (Class B Units [Member], USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013
Class B Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'
Number of Shares, Beginning Balance (in shares)	417
Number of Shares, Granted (in shares)	58
Number of Shares, Vested (in shares)	-438
Number of Shares, Forfeited (in shares)	-37
Number of Shares, Ending Balance (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]	'
Weighted-Average Grant date Fair Value, Beginning Balance (in dollars per share)	$89.99
Weighted-Average Grant date Fair Value, Granted (in dollars per share)	$73.54
Weighted-Average Grant date Fair Value, Vested (in dollars per share)	$87.86
Weighted-Average Grant date Fair Value, Forfeited (in dollars per share)	$89.28
Weighted-Average Grant date Fair Value, Ending Balance (in dollars per share)	'

StockBased_Compensation_Class_1

Stock-Based Compensation - Class E Units (Details) (Class E Units [Member], USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013
Class E Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'
Number of Shares, Beginning Balance (in shares)	476
Number of Shares, Granted (in shares)	0
Number of Shares, Vested (in shares)	-442
Number of Shares, Forfeited (in shares)	-34
Number of Shares, Ending Balance (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]	'
Weighted-Average Grant date Fair Value, Beginning Balance (in dollars per share)	$36.78
Weighted-Average Grant date Fair Value, Granted (in dollars per share)	$0
Weighted-Average Grant date Fair Value, Vested (in dollars per share)	$37.24
Weighted-Average Grant date Fair Value, Forfeited (in dollars per share)	$30.89

StockBased_Compensation_Compen2

Stock-Based Compensation - Compensation Expense (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Compensation expense	$22,306	$13,584	$41,324
Class B and E Units [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Compensation expense	19,860	12,320	40,466
Incentive Units [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Compensation expense	$2,446	$1,264	$858

Employee_Benefit_Plan_Addition

Employee Benefit Plan - Additional Information (Detail) (Parent Company [Member])	12 Months Ended
	Dec. 31, 2013
Parent Company [Member]	'
Employee Benefit Plans [Line Items]	'
Employer contribution match to employee contributions	100.00%

Employee_Benefit_Plan_Total_Ye

Employee Benefit Plan - Total Yearly Expenses of Employee Benefit Plan (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]	'
Defined contribution plan, annual cost recognized	$2,959

Income_Taxes_Benefit_Provision

Income Taxes - (Benefit) Provision for Income Taxes from Continuing Operations (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
U.S. federal	($194)	($627)	$2,047
U.S. state and local	2,902	618	1,218
Non U.S.	3,773	8,708	29,910
Current Income Tax Expense (Benefit)	6,481	8,699	33,175
U.S. federal	-108,077	1,771	-949
U.S. state and local	0	1,046	-263
Non U.S.	-599	-1,240	-1,122
Deferred Income Tax Expense (Benefit)	-108,676	1,577	-2,334
Provision (benefit) for income taxes	($102,195)	$10,276	$30,841

Income_Taxes_Effective_Income_

Income Taxes - Effective Income Tax Reconciliation (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Tax Disclosure [Abstract]	'		'		'
U.S. federal statutory income tax (benefit) expense	$6,235		$9,249		$67,739
Income not subject to U.S. corporate income tax	-14,071		-7,095		-65,718
U.S. state and local income taxes, net of U.S. federal income tax effect	1,886		772		478
Deferred tax benefit resulting from the Company becoming subject to U.S. corporate income taxes	-103,499		0		0
Nondeductible expenses (1)	3,627	[1]	200	[1]	133
Foreign taxes	3,603		7,468		29,118
Other, net	24		-318		-909
Provision (benefit) for income taxes	($102,195)		$10,276		$30,841
[1]	Nondeductible expenses include nondeductible compensation and meals and entertainment.

Income_Taxes_Components_of_Def

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]	'	'
Employee compensation and benefit plans	$16,629	$527
Fixed assets and other amortizable assets	90,130	3,742
Reserves	4,362	0
Valuation of investments	31,154	0
Net operating loss carryforwards, net	125,728	1,041
Less: Valuation allowance on net operating loss carryforwards	-36,043	0
Total deferred tax assets	231,960	5,310
Employee compensation and benefit plans	0	502
Fixed assets and other amortizable assets	29,077	2,558
Valuation of investments	10,414	1,831
Reduction in foreign tax credit for Non-U.S. NOL carryforwards	18,885	0
Total deferred tax liabilities	58,376	4,891
Net deferred tax assets	$173,584	$419

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Jul. 02, 2013	Dec. 31, 2013
				State and Local Jurisdiction [Member]	Foreign Tax Authority [Member]	Domestic Tax Authority [Member]	Knight [Member]	Knight [Member]	Knight [Member]
									Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]	'	'	'	'	'	'	'	'	'
Net deferred tax assets	$173,584,000	$419,000	'	'	'	'	'	'	'
Deferred tax asset, net	'	'	'	'	'	'	'	62,329,000	'
Deferred tax benefit resulting from the Company becoming subject to U.S. corporate income taxes	103,499,000	0	0	'	'	'	'	'	'
Operating loss carryforwards	194,500,000	'	'	'	86,400,000	'	89,000,000	'	65,700,000
Deferred tax assets, operating loss carryforwards	68,100,000	'	'	'	'	'	'	'	'
Deferred tax assets, valuation allowance	6,800,000	'	'	'	'	'	'	'	'
Deferred income tax asset	'	4,200,000	'	'	19,100,000	18,900,000	'	'	'
Deferred tax liabilities, gross	'	3,800,000	'	'	'	'	'	'	'
General business carry forward	2,500,000	'	'	'	'	'	'	'	'
AMT Carryforward	'	'	'	6,800,000	'	'	'	'	'
Unrecognized tax benefits that would impact effective tax rate if recognized	$1,500,000	'	'	'	'	'	'	'	'

Income_Taxes_Schedule_of_Recon

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'
Balance at beginning of period	$0
Increases based on tax positions related to prior periods (1)	1,464	[1]
Decreases based on tax positions related to prior periods	0
Decreases related to settlements with taxing authorities	0
Balance at the end of the period	$1,464
[1]	Increases relate to unrecognized tax benefits that inure to the Company as a result of the Mergers.

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'		'
Beginning Balance	$114,319,000		$0
Other comprehensive income (loss)	15,054,000		114,319,000
Amount reclassified from Accumulated Other Comprehensive Income	-127,972,000	[1]	'
Net current-period other comprehensive loss	-112,918,000		'
Ending Balance	1,401,000		114,319,000
Unrealized gains on Available-for-sale Securities [Member]	'		'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'		'
Beginning Balance	114,319,000		0
Other comprehensive income (loss)	13,689,000		114,319,000
Amount reclassified from Accumulated Other Comprehensive Income	-127,972,000	[1]	'
Net current-period other comprehensive loss	-114,283,000		'
Ending Balance	36,000		114,319,000
Foreign Currency translation adjustments [Member]	'		'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'		'
Beginning Balance	0		0
Other comprehensive income (loss)	1,365,000		0
Amount reclassified from Accumulated Other Comprehensive Income	0	[1]	'
Net current-period other comprehensive loss	1,365,000		'
Ending Balance	1,365,000		0
Investment Income [Member]	'		'
Accumulated Other Comprehensive Income [Line Items]	'		'
Gain on investments	$128,000,000		'
[1]	As a result of the Mergers, the Company recorded a non-cash gain of $128.0 million on its investment in Knight Common Stock, which it recognized within Investment income and other, net on the Consolidated Statements of Operations for the year ended December 31, 2013 and reversed any previous unrealized gains out of Other comprehensive income.

Writedowns_and_Other_Charges_A

Writedowns and Other Charges - Additional Information (Detail) (USD $)	12 Months Ended							3 Months Ended	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013
							Excess Real Estate Capacity [Member]	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]	Leasehold improvements [Member]
Writedown Of Asset And Lease Loss Accrual [Line Items]	'		'		'		'	'	'	'
Write off of deferred debt issuance cost	$16,832,000	[1]	$276,000	[1]	$0	[1]	'	$13,200,000	'	'
Early principal payments	'		'		'		'	300,000,000	300,000,000	'
Asset impairment charges	'		'		'		'	'	'	7,700,000
Writedown of assets and lease loss accrual	'		'		'		$7,100,000	'	'	'
[1]	included in Other expense

Earnings_Per_Share_Additional_

Earnings Per Share - Additional Information (Detail)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Options excluded (in shares)	29.1

Earnings_Per_Share_Reconciliat

Earnings Per Share - Reconciliation of Numerators and Denominators of Basic and Diluted (Loss) Earnings Per Computations (Detail) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]	'	'	'
Income from continuing operations, net of tax	$120,008	$16,151	$162,700
Income from continuing operations and shares used in diluted calculations	120,008	16,151	162,700
Shares used in basic calculations (in shares)	80,143	48,970	50,688
Effect of dilutive stock based awards (in shares)	872	0	0
(Loss) Income and shares used in diluted calculations (in shares)	81,015	48,970	50,688
Net (loss) income allocated to preferred and participating units	-21,565	1,092	12,510
Net Income (Loss) Available to Common Stockholders, Basic, Continuing Operations	141,573	15,059	150,190
Net Income (Loss) Available to Common Stockholders, Basic	$141,653	$15,059	$150,190
Basic earnings per share from continuing operations (in dollars per share)	$1.77	$0.31	$2.96
Diluted earnings per share from continuing operations (in dollars per share)	$1.75	$0.31	$2.96

Significant_Clients_Additional

Significant Clients - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	Client	Client	Client
Risks and Uncertainties [Abstract]	'	'	'
Number of significant clients	0	0	0
Percentage of dollar value traded	10.00%	10.00%	10.00%

Recovered_Sheet1

Commitments and Contingent liabilities - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended		3 Months Ended	1 Months Ended	0 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Aug. 06, 2012	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Oct. 31, 2013	Dec. 31, 2013	Mar. 22, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013
		director		Facebook IPO [Member]	Settlement with SEC [Member]	Facebook IPO [Member]	Facebook IPO [Member]	Parent [Member]	Customers [Member]	Revolving Credit Facility [Member]
		lawsuit						Facebook IPO [Member]	Facebook IPO [Member]
Loss Contingencies [Line Items]	'	'	'	'	'	'	'	'	'	'
Number of putative class action lawsuits	'	2	'	'	'	'	'	'	'	'
Number of derivative lawsuits	'	1	'	'	'	'	'	'	'	'
Raise In equity financing	$400	'	'	'	'	'	'	'	'	'
Number of directors accused of breaking fiduciary duties	'	7	'	'	'	'	'	'	'	'
Pre-tax loss settlements realized	'	'	457.6	'	'	'	'	'	'	'
Litigation settlement	'	'	'	'	12	'	'	'	'	'
Restructuring charge	'	'	'	35.4	'	'	'	'	'	'
Claims limitation related to IPO	'	'	'	'	'	'	62	'	'	'
Proceeds from legal settlements	'	'	'	'	'	12	'	10.5	1.5	'
Weighted average interest rate	'	'	'	'	'	'	'	'	'	3.85%
Rental expense	'	16	9	'	'	'	'	'	'	'
Letters of credit held in escrow	'	$1	'	'	'	'	'	'	'	'
Debt term	'	'3 years	'	'	'	'	'	'	'	'

Recovered_Sheet2

Commitments and Contingent liabilities - Schedule of Capital Lease and Contract Obligations (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]	'
2014	$8,222
2015	2,072
Total	$10,294

Commitments_and_Contingent_lia2

Commitments and Contingent liabilities - Schedule of Interest Expense (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Commitments and Contingencies Disclosure [Abstract]	'	'	'
Interest expense - Capital leases	$700	$1,376	$982

Commitments_and_Contingent_lia3

Commitments and Contingent liabilities - Schedule of Operating Lease and Contract Obligations (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Gross Lease Obligations [Member]	'
Sale Leaseback Transaction [Line Items]	'
Year ending December 31, 2014	$29,689
Year ending December 31, 2015	27,915
Year ending December 31, 2016	27,571
Year ending December 31, 2017	27,036
Year ending December 31, 2018	26,492
Thereafter through December 31, 2027	75,552
Total Amount Of Lease & Contract Obligations	214,255
Sublease Income [Member]	'
Sale Leaseback Transaction [Line Items]	'
Year ending December 31, 2014	4,315
Year ending December 31, 2015	4,914
Year ending December 31, 2016	4,850
Year ending December 31, 2017	4,426
Year ending December 31, 2018	2,720
Thereafter through December 31, 2027	12,521
Total Amount Of Lease & Contract Obligations	33,746
Net Lease Obligations [Member]	'
Sale Leaseback Transaction [Line Items]	'
Year ending December 31, 2014	25,374
Year ending December 31, 2015	23,001
Year ending December 31, 2016	22,721
Year ending December 31, 2017	22,610
Year ending December 31, 2018	23,772
Thereafter through December 31, 2027	63,031
Total Amount Of Lease & Contract Obligations	$180,509

Net_capital_requirements_Net_C

Net capital requirements - Net Capital Levels and Requirements for U.S. Registered Broker-Dealer Subsidiary (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Net Capital and Net Capital Requirements For Company's Broker Dealer Subsidiaries [Line Items]	'
Net Capital	$157,254
Net Capital Requirement	80,900
Excess Net Capital	76,354
Knight Capital Americas LLC [Member]	'
Net Capital and Net Capital Requirements For Company's Broker Dealer Subsidiaries [Line Items]	'
Net Capital	396,655
Net Capital Requirement	22,300
Excess Net Capital	374,355
OCTEG LLC [Member]	'
Net Capital and Net Capital Requirements For Company's Broker Dealer Subsidiaries [Line Items]	'
Net Capital	98,737
Net Capital Requirement	1,000
Excess Net Capital	97,737
GETCO EXECUTION SERVICES, LLC [Member]	'
Net Capital and Net Capital Requirements For Company's Broker Dealer Subsidiaries [Line Items]	'
Net Capital	11,433
Net Capital Requirement	250
Excess Net Capital	$11,183

Net_capital_requirements_Finan

Net capital requirements - Financial Resource Requirements on Significant Foreign Regulated Broker-Dealer (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Net Capital Requirements [Line Items]	'
Financial Resources	$157,254
Resource Requirement	80,900
Excess Financial Resources	76,354
Knight Capital Europe Limited [Member]	'
Net Capital Requirements [Line Items]	'
Financial Resources	97,892
Resource Requirement	$65,967

Financial_instruments_with_Off1

Financial instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]	'	'
Loans outstanding	$657,259,000	$15,000,000
Executive Director or Officer [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Loans outstanding	$0	'

Business_Segments_Income_Loss_

Business Segments - Income (Loss) from Continuing Operations Before Income Taxes ("Pre-Tax Earnings") and Total Assets by Segment (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'
Revenues	$1,020,171	$551,234	$915,448
Pre-tax earnings	17,813	26,427	193,541
Total assets	6,991,215	1,687,536	1,302,355
Market Making [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Revenues	688,197	495,427	862,760
Pre-tax earnings	103,559	34,887	203,886
Total assets	3,939,965	1,408,516	1,191,724
Global Execution Services [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Revenues	197,766	36,211	27,599
Pre-tax earnings	-25,739	-7,330	-15,406
Total assets	1,106,448	33,623	19,928
Corporate and Other [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Revenues	134,208	19,596	25,089
Pre-tax earnings	-60,007	-1,130	5,061
Total assets	1,944,802	245,397	90,703
UNITED STATES	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Revenues	827,245	340,117	489,514
International [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Revenues	$192,926	$211,117	$425,934

Subsequent_Events_Details

Subsequent Events (Details) (USD $)

12 Months Ended

3 Months Ended

12 Months Ended

2 Months Ended

0 Months Ended

7 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Mar. 03, 2014

Jan. 22, 2014

Jan. 22, 2014

Jan. 31, 2014

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

BATS Global Markets and Direct Edge Holdings LLC [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Subsequent Event [Member]

Subsequent Event [Line Items]

'

'

'

'

'

'

'

'

'

Principal payment

'

'

'

$300,000,000

$300,000,000

'

$100,000,000

$400,000,000

'

Write off of deferred debt issuance cost

16,832,000

[1]

276,000

[1]

0

[1]

13,200,000

'

4,200,000

'

'

'

First periodic payment amount

'

'

'

'

'

'

235,000,000

235,000,000

'

Amount outstanding

'

'

'

'

'

'

135,000,000

135,000,000

'

Dividends Receivable, Contingent Upon Merger

'

'

'

'

'

'

'

'

$41,700,000

[1]

included in Other expense

Condensed_Financial_Statements2

Condensed Financial Statements of Knight Capital Group, Inc. (parent only) - Statements of Financial Condition (Parent Only) (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets	'	'	'	'
Cash and cash equivalents	$674,281,000	$427,631,000	$607,689,000	$614,025,000
Deferred tax asset	173,584,000	4,180,000	'	'
Other assets	147,322,000	16,806,000	'	'
Total assets	6,991,215,000	1,687,536,000	'	'
Liabilities	'	'	'	'
Accrued expenses and other liabilities	172,406,000	118,068,000	'	'
Debt	657,259,000	15,000,000	'	'
Total liabilities	5,483,963,000	721,725,000	'	'
Redeemable preferred member's equity	0	311,139,000	'	'
Total equity	1,507,252,000	654,672,000	'	'
Total liabilities, redeemable preferred member's equity and equity	6,991,215,000	1,687,536,000	'	'
Parent Company [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	253,017,000	114,511,000	'	'
Financial instruments owned, at fair value	0	'	'	'
Receivable from subsidiaries	60,460,000	'	'	'
Investments in subsidiaries	1,356,412,000	'	'	'
Income taxes receivable	90,000	'	'	'
Goodwill and intangible assets, less accumulated amortization	0	'	'	'
Deferred tax asset	144,109,000	'	'	'
Subordinated loans to subsidiaries	250,000,000	'	'	'
Other assets	21,182,000	'	'	'
Total assets	2,085,270,000	'	'	'
Liabilities	'	'	'	'
Payable to subsidiaries	25,705,000	'	'	'
Accrued expenses and other liabilities	12,313,000	'	'	'
Debt	540,000,000	'	'	'
Total liabilities	578,018,000	'	'	'
Redeemable preferred member's equity	0	'	'	'
Total equity	1,507,252,000	'	'	'
Total liabilities, redeemable preferred member's equity and equity	2,085,270,000	'	'	'
GETCO Holding Company [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	'	114,511,000	112,496,000	163,706,000
Financial instruments owned, at fair value	'	2,000	'	'
Receivable from subsidiaries	'	216,266,000	'	'
Investments in subsidiaries	'	773,818,000	'	'
Income taxes receivable	'	0	'	'
Goodwill and intangible assets, less accumulated amortization	'	8,132,000	'	'
Deferred tax asset	'	0	'	'
Subordinated loans to subsidiaries	'	0	'	'
Other assets	'	1,039,000	'	'
Total assets	'	1,113,768,000	'	'
Liabilities	'	'	'	'
Payable to subsidiaries	'	47,998,000	'	'
Accrued expenses and other liabilities	'	84,959,000	'	'
Debt	'	15,000,000	'	'
Total liabilities	'	147,957,000	'	'
Redeemable preferred member's equity	'	311,139,000	'	'
Total equity	'	654,672,000	'	'
Total liabilities, redeemable preferred member's equity and equity	'	$1,113,768,000	'	'

Condensed_Financial_Statements3

Condensed Financial Statements of Knight Capital Group, Inc. (parent only) - Statements of Operations (Parent Only) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Revenues	'		'		'
Investment income and other, net	$116,930		$27,010		$20,194
Total revenues	1,020,171		551,234		915,448
Expenses	'		'		'
Employee compensation and benefits	349,192		157,855		241,753
Interest	44,785		2,665		1,299
Depreciation and amortization	55,570		34,938		45,675
Professional fees	46,662		14,072		17,142
Write off of deferred debt issuance cost	16,832	[1]	276	[1]	0	[1]
Other	43,094		23,073		26,587
Total expenses	1,002,358		524,807		721,907
Income from continuing operations before income taxes	17,813		26,427		193,541
Provision (benefit) for income taxes	-102,195		10,276		30,841
Income from continuing operations, net of tax	120,008		16,151		162,700
Net income	120,088		16,151		162,700
Parent Company [Member]	'		'		'
Revenues	'		'		'
Investment income and other, net	3,717		'		'
Total revenues	3,717		'		'
Expenses	'		'		'
Employee compensation and benefits	31,970		'		'
Interest	28,476		'		'
Depreciation and amortization	698		'		'
Professional fees	30,488		'		'
Write off of deferred debt issuance cost	9,268		'		'
Other	20,561		'		'
Total expenses	121,461		'		'
Income from continuing operations before income taxes	-117,744		'		'
Provision (benefit) for income taxes	-120,761		'		'
Income from continuing operations, net of tax	3,017		'		'
Equity in earnings of subsidiaries	117,071		'		'
Net income	120,088		'		'
GETCO Holding Company [Member]	'		'		'
Revenues	'		'		'
Investment income and other, net	'		5,981		2,001
Total revenues	'		5,981		2,001
Expenses	'		'		'
Employee compensation and benefits	'		-12,251		7,023
Interest	'		1,195		256
Depreciation and amortization	'		1,395		698
Professional fees	'		4,997		1,484
Write off of deferred debt issuance cost	'		336		286
Other	'		1,157		852
Total expenses	'		-3,171		10,599
Income from continuing operations before income taxes	'		9,152		-8,598
Provision (benefit) for income taxes	'		0		0
Income from continuing operations, net of tax	'		9,152		-8,598
Equity in earnings of subsidiaries	'		6,999		171,298
Net income	'		$16,151		$162,700
[1]	included in Other expense

Condensed_Financial_Statements4

Condensed Financial Statements of Knight Capital Group, Inc. (parent only) - Statements of Cash Flows (Parent Only) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities	'	'	'
Net income	$120,088	$16,151	$162,700
Adjustments to reconcile net income to net cash used in operating activities	'	'	'
Writedown and amortization of debt issuance costs	17,332	276	0
Amortization of intangibles	-19,211	-5,518	-3,595
Financial instruments owned, at fair value	-129,035	-414,537	-140,414
Deferred tax benefit	-103,499	0	0
Other assets	24,703	1,332	-2,922
(Decrease) increase in operating liabilities	'	'	'
Accrued expenses and other liabilities	-64,470	-13,779	4,472
Net cash provided by (used in) operating activities	141,204	-64,516	210,282
Cash flows from investing activities	'	'	'
Acquisition of Automat Limited	-27,703	-31,389	-62,790
Net cash provided by investing activities	582,892	-46,501	-109,634
Cash flows from financing activities	'	'	'
Partial repayment of Credit Agreement	-300,000	0	0
Proceeds from issuance of notes payable	0	0	15,000
Repayment of notes payable	-15,000	'	'
Payment of debt issuance cost	-34,592	-1,375	0
Issuance of equity to General Atlantic	55,000	0	0
Payment to former Knight Capital Group, Inc. stockholders	-720,000	0	0
Repayment of Knight Convertible Notes	-305,000	0	0
Funding of collateral account for Knight Convertible Notes	-117,259	0	0
Payment out of collateral account for Knight Convertible Notes	117,259	0	0
Members' distributions	-21,002	-37,061	-122,227
Cost of common stock repurchased	-11,324	0	0
Net cash used in financing activities	-478,811	-69,041	-106,984
Increase in cash and cash equivalents	246,650	-180,058	-6,336
Cash and cash equivalents at beginning of period	427,631	607,689	614,025
Cash and cash equivalents at end of period	674,281	427,631	607,689
Supplemental disclosure of cash flow information:	'	'	'
Cash paid for interest	56,227	8,084	3,641
Cash paid for income taxes	10,198	21,789	31,114
Parent Company [Member]	'	'	'
Cash flows from operating activities	'	'	'
Net income	120,088	'	'
Adjustments to reconcile net income to net cash used in operating activities	'	'	'
Equity in earnings of subsidiaries	-117,071	'	'
Writedown and amortization of debt issuance costs	16,931	'	'
Amortization of intangibles	-698	'	'
Financial instruments owned, at fair value	-250,000	'	'
Receivable from subsidiaries	-67,523	'	'
Deferred tax benefit	-144,109	'	'
Income taxes receivable	-90	'	'
Other assets	-15,351	'	'
(Decrease) increase in operating liabilities	'	'	'
Payable to subsidiaries	-2,024	'	'
Accrued expenses and other liabilities	59,921	'	'
Net cash provided by (used in) operating activities	-398,530	'	'
Cash flows from investing activities	'	'	'
Cash acquired upon acquisition of Knight Capital Group, Inc.	509,133	'	'
Cash received from sale of Urban Financial of America, LLC	85,406	'	'
Acquisition of Automat Limited	0	'	'
Dividends received from subsidiaries	646,425	'	'
Capital contributions to subsidiaries	-238,909	'	'
Net cash provided by investing activities	1,002,055	'	'
Cash flows from financing activities	'	'	'
Proceeds from issuance of Credit Agreement	535,000	'	'
Partial repayment of Credit Agreement	-300,000	'	'
Proceeds from issuance of Senior Secured Notes	305,000	'	'
Proceeds from issuance of notes payable	0	'	'
Repayment of notes payable	-15,000	'	'
Payment of debt issuance cost	-34,952	'	'
Issuance of equity to General Atlantic	55,000	'	'
Payment to former Knight Capital Group, Inc. stockholders	-720,000	'	'
Repayment of Knight Convertible Notes	257,741	'	'
Funding of collateral account for Knight Convertible Notes	-117,259	'	'
Payment out of collateral account for Knight Convertible Notes	117,259	'	'
Proceeds from stock issuance	0	'	'
Members' distributions	-21,002	'	'
Cost of common stock repurchased	-11,324	'	'
Net cash used in financing activities	-465,019	'	'
Increase in cash and cash equivalents	138,506	'	'
Cash and cash equivalents at beginning of period	114,511	'	'
Cash and cash equivalents at end of period	253,017	'	'
Supplemental disclosure of cash flow information:	'	'	'
Cash paid for interest	26,239	'	'
Cash paid for income taxes	365	'	'
GETCO Holding Company [Member]	'	'	'
Cash flows from operating activities	'	'	'
Net income	'	16,151	162,700
Adjustments to reconcile net income to net cash used in operating activities	'	'	'
Equity in earnings of subsidiaries	'	-6,999	-171,298
Writedown and amortization of debt issuance costs	'	52	0
Amortization of intangibles	'	-1,395	-698
Financial instruments owned, at fair value	'	0	0
Receivable from subsidiaries	'	-97,375	-89,814
Deferred tax benefit	'	0	0
Income taxes receivable	'	0	0
Other assets	'	31,031	48,653
(Decrease) increase in operating liabilities	'	'	'
Payable to subsidiaries	'	11,756	33,932
Accrued expenses and other liabilities	'	5,106	718
Net cash provided by (used in) operating activities	'	-38,883	-14,411
Cash flows from investing activities	'	'	'
Cash acquired upon acquisition of Knight Capital Group, Inc.	'	0	0
Cash received from sale of Urban Financial of America, LLC	'	0	0
Acquisition of Automat Limited	'	0	-10,975
Dividends received from subsidiaries	'	161,606	127,530
Capital contributions to subsidiaries	'	-70,794	-84,928
Net cash provided by investing activities	'	90,812	31,627
Cash flows from financing activities	'	'	'
Proceeds from issuance of Credit Agreement	'	0	0
Partial repayment of Credit Agreement	'	0	0
Proceeds from issuance of Senior Secured Notes	'	0	0
Proceeds from issuance of notes payable	'	0	15,000
Repayment of notes payable	'	0	0
Payment of debt issuance cost	'	0	0
Issuance of equity to General Atlantic	'	0	0
Payment to former Knight Capital Group, Inc. stockholders	'	0	0
Repayment of Knight Convertible Notes	'	0	0
Funding of collateral account for Knight Convertible Notes	'	0	0
Payment out of collateral account for Knight Convertible Notes	'	0	0
Proceeds from stock issuance	'	12,320	41,365
Members' distributions	'	-62,234	-124,791
Cost of common stock repurchased	'	0	0
Net cash used in financing activities	'	-49,914	-68,426
Increase in cash and cash equivalents	'	2,015	-51,210
Cash and cash equivalents at beginning of period	'	112,496	163,706
Cash and cash equivalents at end of period	'	114,511	112,496
Supplemental disclosure of cash flow information:	'	'	'
Cash paid for interest	'	1,116	92
Cash paid for income taxes	'	$0	$0