Condensed Consolidated Statements of Financial Condition (unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Cash and securities segregated, at cost	$ 723,470	$ 565,264
Limited partners, units issued	270,638,334	272,301,827
Limited partners, units outstanding	270,638,334	272,301,827