Investments of Operating Entities and Consolidated Funds - Securities borrowed and securities loaned (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Securities Borrowed, Gross		$ 598,090	$ 443,148
Gross amounts offset on the Condensed Consolidated Statements of Financial Condition (a)	[1]	0	0
Gross amounts recognized		598,090	443,148
Securities borrowed, additional amounts, asset		0	0
Financial instruments		577,017	414,778
Cash Collateral pledged (b)		0	0
Net amounts		21,073	28,370
Securities Loaned, Gross		462,854	456,831
Gross amounts offset on the Condensed Consolidated Statements of Financial Condition (a)	[1]	0	0
Gross amounts recognized		462,854	456,831
Additional Amounts Available		0	0
Financial instruments		445,271	439,228
Cash Collateral pledged (b)		0	0
Net amounts		$ 17,583	$ 17,603

[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.