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

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Merger of GETCO and Knight - Intangible Assets Acquired (Details) - USD ($) $ in Thousands		12 Months Ended
	Jul. 01, 2013	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill		$ 16,404	$ 17,311
Amortization Years		3 years	5 years
Knight
Business Acquisition [Line Items]
Intangible assets	$ 155,425
Goodwill	12,666
Total	168,091
Knight \| Technology
Business Acquisition [Line Items]
Intangible assets	$ 110,504
Amortization Years	5 years
Knight \| Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 35,000
Knight \| Customer relationships \| Minimum
Business Acquisition [Line Items]
Amortization Years	9 years
Knight \| Customer relationships \| Maximum
Business Acquisition [Line Items]
Amortization Years	11 years
Knight \| Trade names
Business Acquisition [Line Items]
Intangible assets	$ 4,000
Amortization Years	10 years
Knight \| Trading rights
Business Acquisition [Line Items]
Intangible assets	$ 5,921
Amortization Years	7 years