Investments of Operating Entities and Consolidated Funds - Securities borrowed and securities loaned (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Securities borrowed		$ 1,228,036	$ 407,795
Securities Borrowed, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	[1]	0	0
Securities borrowed, net amounts included on the condensed consolidated statements of financial condition		1,228,036	407,795
Securities borrowed, additional amounts, asset		0	0
Securities Borrowed, Collateral, Obligation to Return Securities		1,209,672	383,593
Securities Borrowed, Collateral, Obligation to Return Cash	[2]	0	0
Securities Borrowed, Amount Offset Against Collateral		18,364	24,202
Securities borrowed, cash collateral pledged		0
Securities Loaned		1,339,647	414,852
Securities Loaned, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	[1]	0	0
Securities Loaned, Gross amounts recognized		1,339,647	414,852
Securities Loaned, Additional Amounts Available		0	0
Securities Loaned, Collateral, Right to Reclaim Securities		1,282,340	391,310
Securities Loaned, Collateral, Right to Reclaim Cash	[2]	0	0
Securities Loaned, Amount Offset Against Collateral		57,307	23,542
Securities Sold under Agreements to Repurchase, Asset		23,772
Securities Loaned, Financial instruments		25,635
Securities Loaned, Net amounts		(1,863)
Securities Sold under Agreements to Repurchase		23,772	$ 0
Securities Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement		0
Securities sold under agreements to repurchase, additional amounts		$ 0

[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.

[2] Includes the amount of cash collateral held/posted.