Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Cash and securities segregated, at cost	$ 1,877,798,000	$ 1,090,443,000
Limited partners, units issued (in units)	268,620,187	270,380,314
Limited partners, units outstanding (in units)	268,620,187	270,380,314