Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Cash and securities segregated, at cost	$ 1,169,461	$ 816,350
Capital:
Limited partners units issued (in units)	268,850,276	268,659,333
Limited partners, units outstanding (in units)	268,850,276	268,659,333