Slicers (applies to each fact value in each table cell)

Reporting Entity [Axis]

0001569391 (http://www.sec.gov/CIK)

Fair Value Disclosures [Abstract]	Period [Axis]
	2016-01-01 - 2016-12-31
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 December 31, 2016   Level 1   Level 2   Level 3   Total Assets                 Financial instruments owned, at fair value:                 Equities   $ 2,343,033   $ —   $ —   $ 2,343,033 Corporate debt   127,237   —   —   127,237 U.S. government and Non-U.S. government obligations   50,461   —   —   50,461 Listed options   19,100   —   —   19,100 Foreign currency forward contracts   —   30   —   30 Total Financial instruments owned, at fair value   2,539,831   30   —   2,539,861 Investments(1)   9,198   —   —   9,198 Other (2)   —   62,824   2,846   65,670 Total assets held at fair value   $ 2,549,029   $ 62,854   $ 2,846   $ 2,614,729 Liabilities           Financial instruments sold, not yet purchased, at fair value:                 Equities   $ 1,821,957   $ —   $ —   $ 1,821,957 Corporate debt   123,561   —   —   123,561 U.S. government and Non-U.S. government obligations   87,661   —   —   87,661 Listed options   12,961   —   —   12,961 Total liabilities held at fair value   $ 2,046,140   $ —   $ —   $ 2,046,140 (1)  Investments comprise our investments in CME Group and Bats and are included within Investments on the Consolidated Statements of Financial Condition. See Footnote 9 "Investments" for additional information. (2)  Other primarily consists of a $60.5 million receivable from Bats related to the sale of KCG Hotspot and a $2.8 million receivable from the sale of an investment, both of which are included within Other Assets, and $2.3 million primarily related to deferred compensation investments which is included within Investments on the Consolidated Statements of Financial Condition.     Assets and Liabilities Measured at Fair Value on a Recurring Basis December 31, 2015   Level 1   Level 2   Level 3   Total Assets                 Financial instruments owned, at fair value:                 Equities   $ 2,129,208   $ —   $ —   $ 2,129,208 Listed options   178,360   —   —   178,360 U.S. government and Non-U.S. government obligations   41,706   —   —   41,706 Corporate debt   94,681   —   —   94,681 Foreign currency forward contracts   —   445   —   445 Total Financial instruments owned, at fair value   2,443,955   445   —   2,444,400 Investment in CME Group (1)   1,814   —   —   1,814 Other (2)   —   65,732   5,789   71,521 Total assets held at fair value   $ 2,445,769   $ 66,177   $ 5,789   $ 2,517,735 Liabilities                 Financial instruments sold, not yet purchased, at fair value:                 Equities   $ 1,856,171   $ —   $ —   $ 1,856,171 Listed options   151,893   —   —   151,893 U.S. government obligations   21,056   —   —   21,056 Corporate debt   84,284   —   —   84,284 Total liabilities held at fair value   $ 2,113,404   $ —   $ —   $ 2,113,404 (1)  Investment in CME Group is included within Investments on the Consolidated Statements of Financial Condition. See Footnote 9 "Investments" for additional information. (2)  Other primarily consists of a $64.2 million receivable from Bats related to the sale of KCG Hotspot and a $5.8 million receivable from the sale of an investment, both of which are included in Other assets, and $1.5 million primarily related to deferred compensation investments which is included within Investments on the Consolidated Statements of Financial Condition.
Changes in Fair Value of Financial Assets Categorized within Level 3	The following is a summary of changes in fair value of the Company's financial assets that have been categorized within Level 3 of the fair value hierarchy at December 31, 2016 and 2015 (in thousands):   Level 3 Financial Assets for the year ended December 31, 2016   Balance at January 1, 2016   Realized gains(losses) during period   Unrealized gains (losses) during the period   Purchases   Sales   Settlements   Issuances   Transfers in or (out) of Level 3   Balance at December 31, 2016 Receivable from sold investment $ 5,789   $ —   $ 980   $ —   $ —   $ (3,923 )   $ —   $ —   $ 2,846   Level 3 Financial Assets for the year ended December 31, 2015   Balance at January 1, 2015   Realized gains(losses) during period   Unrealized gains (losses) during the period   Purchases   Sales   Settlements   Issuances   Transfers in or (out) of Level 3   Balance at December 31, 2015 Receivable from sold investment $ —   $ —   $ —   $ —   $ —   $ —   $ 5,789   $ —   $ 5,789