Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
REVENUE	$ 39,580	$ 36,229	$ 117,180	$ 102,386
Asset-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	19,578	19,407	58,820	55,593
Performance-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	0	349	0	410
Separately Managed Accounts
Disaggregation of Revenue [Line Items]
REVENUE	19,578	19,756	58,820	56,003
Asset-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	15,860	13,493	46,772	38,157
Decrease in Asset-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	0	0	0	0
Performance-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	756	580	2,551	1,280
Sub-Advised Accounts
Disaggregation of Revenue [Line Items]
REVENUE	16,616	14,073	49,323	39,437
Asset-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	3,537	2,400	9,658	6,946
Expense Cap Reimbursements
Disaggregation of Revenue [Line Items]
REVENUE	(151)	0	(633)	0
Performance-Based Fees
Disaggregation of Revenue [Line Items]
REVENUE	0	0	12	0
Pzena Funds
Disaggregation of Revenue [Line Items]
REVENUE	$ 3,386	$ 2,400	$ 9,037	$ 6,946