The amount of identifiable intangible assets recognized as of the acquisition date.

+ References+ Details

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Merger of GETCO and Knight - Intangible Assets Acquired (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended		1 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Jul. 02, 2013 Knight [Member]	Jul. 31, 2013 Technology [Member] Knight [Member]	Jul. 02, 2013 Technology [Member] Knight [Member]	Jul. 02, 2013 Customer relationships [Member] Knight [Member]	Jul. 31, 2013 Trade names [Member] Knight [Member]	Jul. 02, 2013 Trade names [Member] Knight [Member]	Jul. 31, 2013 Trading rights [Member] Knight [Member]	Jul. 02, 2013 Trading rights [Member] Knight [Member]	Jul. 31, 2013 Minimum [Member] Customer relationships [Member] Knight [Member]	Jul. 31, 2013 Maximum [Member] Customer relationships [Member] Knight [Member]
Business Acquisition [Line Items]
Amount			$ 156,800		$ 110,000	$ 35,000		$ 4,000		$ 7,800
Goodwill	18,398	4,645	13,753
Total			$ 170,553
Weighted average useful life	7 years	10 years		5 years			10 years		7 years		9 years	11 years