Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 37,410	$ 39,252
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	18,596	20,082
Separately Managed Accounts
Disaggregation of Revenue [Line Items]
Revenues	18,596	20,082
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	14,890	15,565
Decrease in Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	(335)	0
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	452	886
Sub-Advised Accounts
Disaggregation of Revenue [Line Items]
Revenues	15,007	16,451
Asset-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	3,989	2,986
Expense Cap Reimbursements
Disaggregation of Revenue [Line Items]
Revenues	(182)	(279)
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenues	0	12
Pzena Funds
Disaggregation of Revenue [Line Items]
Revenues	$ 3,807	$ 2,719