Condensed Consolidated Statements of Financial Condition (unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Cash and securities segregated, at cost	$ 381,486	$ 476,275
Limited partners, units issued	270,030,040	273,040,452
Limited partners, units outstanding	270,030,040	273,040,452