Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 50,877	$ 30,131	$ 96,748	$ 64,810
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	26,525	16,738	51,072	35,434
Separately Managed Accounts
Disaggregation of Revenue [Line Items]
Revenues	26,525	16,738	51,072	35,434
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	20,350	11,272	37,973	24,995
Impact of Fulcrum Fees
Disaggregation of Revenue [Line Items]
Revenues	(958)	(1,010)	(1,953)	(2,024)
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	8		8	0
Sub-Advised Accounts
Disaggregation of Revenue [Line Items]
Revenues	19,400	10,262	36,028	22,971
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	5,157	3,477	10,109	7,077
Expense Cap Reimbursements
Disaggregation of Revenue [Line Items]
Revenues	(205)	(346)	(461)	(672)
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenues				0
Pzena Funds
Disaggregation of Revenue [Line Items]
Revenues	$ 4,952	$ 3,131	$ 9,648	$ 6,405