Investments of Operating Entities and Consolidated Funds - Securities borrowed and securities loaned (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Securities Borrowed, Gross		$ 443,148,000
Gross amounts offset on the Consolidated Statements of Financial Condition (a)	[1]	0
Gross amounts recognized		443,148,000	$ 0
Securities borrowed, additional amounts, asset		0
Financial instruments		414,778,000
Cash Collateral pledged (b)		0
Net amounts		28,370,000
Securities Loaned, Gross		456,831,000
Gross amounts offset on the Consolidated Statements of Financial Condition (a)	[1]	0
Gross amounts recognized		456,831,000	$ 0
Additional Amounts Available		0
Financial instruments		439,228,000
Cash Collateral pledged (b)		0
Net amounts		$ 17,603,000

[1] Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred.