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

Reporting Entity [Axis]

0001109448 (http://www.sec.gov/CIK)

Fair Value Disclosures [Abstract]	Period [Axis]
	2016-01-01 - 2016-12-31
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities Measured on a Recurring Basis	Valuation of our financial instruments by pricing observability levels as of December 31, 2016 and 2015 was as follows (in thousands):   Level 1   Level 2   Level 3   Total     December 31, 2016:               Money markets $ 107,250   $ —   $ —   $ 107,250 U.S. Treasury Bills —   922,126   —   922,126 Available-for-sale               Equity securities 23   —   —   23 Fixed income securities 22   —   —   22 Trading               Equity securities 158,316   17,785   110   176,211 Fixed income securities 80,473   11,107   —   91,580 Long exchange-traded options 3,106   —   —   3,106 Derivatives 1,224   7,189   —   8,413 Private equity —   —   4,913   4,913 Consolidated VIEs                 Investments 341,830   203,197   5,741   550,768   Derivatives 58   1,739   —   1,797 Total assets measured at fair value $ 692,302   $ 1,163,143   $ 10,764   $ 1,866,209                 Securities sold not yet purchased               Short equities – corporate $ 40,252   $ —   $ —   $ 40,252 Short exchange-traded options 692   —   —   692 Derivatives 1,092   7,557   —   8,649 Consolidated VIEs                  Short equities 248,419   —   —   248,419    Derivatives 48   2,033   —   2,081 Contingent payment arrangements —   —   17,589   17,589 Total liabilities measured at fair value $ 290,503   $ 9,590   $ 17,589   $ 317,682                 December 31, 2015:               Money markets $ 116,445   $ —   $ —   $ 116,445 U.S. Treasury Bills —   485,121   —   485,121 Available-for-sale               Equity securities 181   —   —   181 Fixed income securities 183   —   —   183 Trading               Equity securities 325,248   874   113   326,235 Fixed income securities 170,244   12,532   —   182,776 Long exchange-traded options 5,910   —   —   5,910 Derivatives 1,539   11,049   —   12,588 Private equity 14,305   —   16,035   30,340 Total assets measured at fair value $ 634,055   $ 509,576   $ 16,148   $ 1,159,779                 Securities sold not yet purchased               Short equities – corporate $ 15,254   $ —   $ —   $ 15,254 Short exchange-traded options 843   —   —   843 Derivatives 2,651   9,570   —   12,221 Contingent payment arrangements —   —   31,399   31,399 Total liabilities measured at fair value $ 18,748   $ 9,570   $ 31,399   $ 59,717
Fair Value Measurement Level 3 Reconciliation	The change in carrying value associated with Level 3 financial instruments carried at fair value, classified as private equity investments, trading equity securities and investments held by our consolidated VIEs, is as follows:   December 31, 2016   December 31, 2015   (in thousands) Balance as of beginning of period $ 16,148   $ 27,813 Transfers out (23,566 )   (26 ) Activity related to consolidated VIEs 19,772   — Purchases —   195 Sales —   (14,178 ) Realized gains, net —   1,983 Unrealized (losses) gains, net (1,590 )   361 Balance as of end of period $ 10,764   $ 16,148
Quantitative Information About Private Equity Level 3 Fair Value Measurements	Quantitative information about our consolidated venture capital fund Level 3 fair value measurements as of December 31, 2015 was as follows:   Fair Value as of December 31, 2015   Valuation Technique   Unobservable Input   Range   (in thousands)                             Technology, Media and Telecommunications $ 9,527   Market comparable companies   Revenue multiple   2.5 – 4.8           Marketability discount   30 %
Schedule of Contingent Payment Arrangements Level 3 Financial Instruments	The change in carrying value associated with Level 3 financial instruments carried at fair value, classified as contingent payment arrangements, is as follows:   December 31, 2016   December 31, 2015   (in thousands) Balance as of beginning of period $ 31,399   $ 42,436 Addition 11,893   — Accretion 1,237   1,770 Changes in estimates (21,482 )   (7,211 ) Payments (5,458 )   (5,596 ) Balance as of end of period $ 17,589   $ 31,399