Consolidated Statements of Financial Condition (Parenthetical) - shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred equity, units issued (in units)	12,400,000	12,400,000
Preferred equity, units outstanding (in units)	12,400,000	12,400,000
Partners' Capital units issued (in units)	82,280,033	80,814,732
Partners' Capital units outstanding (in units)	82,280,033	80,814,732