Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 33,948	$ 37,065	$ 98,758	$ 112,318
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	18,457	18,548	53,891	55,959
Separately Managed Accounts
Disaggregation of Revenue [Line Items]
Revenues	18,457	18,548	53,891	55,959
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	12,884	14,777	37,880	44,938
Decrease in Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	(1,004)	(468)	(3,029)	(1,271)
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenues		342		1,048
Sub-Advised Accounts
Disaggregation of Revenue [Line Items]
Revenues	11,880	14,651	34,851	44,715
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	3,808	4,046	10,886	12,130
Expense Cap Reimbursements
Disaggregation of Revenue [Line Items]
Revenues	(197)	(180)	(870)	(486)
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenues				0
Pzena Funds
Disaggregation of Revenue [Line Items]
Revenues	$ 3,611	$ 3,866	$ 10,016	$ 11,644