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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Business Segments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Debt interest expense	$ 36,755	$ 32,456	$ 34,938
Total assets held for sale	25,999	40,484
KCG Hotspot
Segment Reporting Information [Line Items]
Gain from sale of business	373,800
Market Making
Segment Reporting Information [Line Items]
Debt interest expense	21,200	24,700
Market Making \| Businesses Held for Sale
Segment Reporting Information [Line Items]
Total assets held for sale	26,000
Global Execution Services
Segment Reporting Information [Line Items]
Debt interest expense	4,900	7,100
Global Execution Services \| KCG Hotspot
Segment Reporting Information [Line Items]
Total assets held for sale		$ 40,500
Global Execution Services \| Revenues \| KCG Hotspot
Segment Reporting Information [Line Items]
Gain from sale of business	385,000
Global Execution Services \| Pre-tax Earnings \| KCG Hotspot
Segment Reporting Information [Line Items]
Gain from sale of business	$ 373,800