Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and securities segregated, at cost	$ 816,350	$ 946,093
Capital:
Limited partners units issued (in units)	268,659,333	268,893,534
Limited partners, units outstanding (in units)	268,659,333	268,893,534