Revenues from Contracts with Customers - Reconciliation of Revenues Recognized from Contracts with Customers to Total Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Revenues from Contracts with Customers	$ 164,239	$ 129,539	$ 294,468	$ 262,795
Sublease Income and Other	2,465	1,131	292	1,917
Total Revenues	166,704	130,670	294,760	264,712
Advisory Fees
Disaggregation Of Revenue [Line Items]
Revenues from Contracts with Customers	133,035	98,294	237,502	201,757
Total Revenues	133,035	98,294	237,502	201,757
Placement Fees
Disaggregation Of Revenue [Line Items]
Revenues from Contracts with Customers	28,695	28,132	52,007	54,252
Total Revenues	28,695	28,132	52,007	54,252
Interest Income from Placement Fees
Disaggregation Of Revenue [Line Items]
Revenues from Contracts with Customers	927	1,015	2,093	2,420
Reimbursable Expenses
Disaggregation Of Revenue [Line Items]
Revenues from Contracts with Customers	$ 1,582	$ 2,098	$ 2,866	$ 4,366