Compensation Guarantees Payable

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- Definition

Number of Derivative Lawsuits

+ References

No definition available.

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- Definition

Number of Directors Accused of Breaking Fiduciary Duties

+ References

No definition available.

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- Definition

Number of Putative Class Action Lawsuits

+ References

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- Definition

Raise In Equity Financing

+ References

No definition available.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10)

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- Definition

Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

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- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

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- Definition

Weighted average interest rate of long-term debt outstanding.

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- Definition

Number of claims dismissed.

+ References

No definition available.

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Commitments and Contingent liabilities - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Aug. 06, 2012	Aug. 01, 2012 lawsuit	Sep. 26, 2014	Jan. 15, 2013 director	Jun. 05, 2014
Loss Contingencies [Line Items]
Rental expense	$ 19,700,000us-gaap_LeaseAndRentalExpense	$ 16,000,000us-gaap_LeaseAndRentalExpense
Letters of credit held in escrow	11,600,000us-gaap_EscrowDeposit
Compensation guarantees payable	9,200,000kcg_CompensationGuaranteesPayable	0kcg_CompensationGuaranteesPayable
Revolving Credit Facility [Member]
Loss Contingencies [Line Items]
Weighted average interest rate	3.52%
Debt term	3 years
Technology Issue [Member]
Loss Contingencies [Line Items]
Number of putative class action lawsuits				2
Number of class action lawsuit voluntarily dismissed				1
Number of derivative lawsuits				1
Raise In equity financing			400,000,000.0
New York Litigation [Member]
Loss Contingencies [Line Items]
Number of directors accused of breaking fiduciary duties						7
Pre-tax loss settlements realized						457,600,000
Attorneys' fees and costs					425,000
New York Litigation [Member] \| Maximum [Member]
Loss Contingencies [Line Items]
Attorneys' fees and costs							$ 490,000