Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Cash and securities segregated, at cost	$ 665,983	$ 565,264
Limited partners, units issued	268,777,653	272,301,827
Limited partners, units outstanding	268,777,653	272,301,827