Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 64,292	$ 55,833	$ 128,978	$ 119,195
Management and advisory fees
Disaggregation of Revenue [Line Items]
Revenues	59,196	53,248	119,747	104,227
Specialized funds
Disaggregation of Revenue [Line Items]
Revenues	26,985	22,736	53,944	43,751
Customized separate accounts
Disaggregation of Revenue [Line Items]
Revenues	22,466	21,106	44,429	41,493
Advisory
Disaggregation of Revenue [Line Items]
Revenues	5,961	6,152	12,213	12,361
Reporting and other
Disaggregation of Revenue [Line Items]
Revenues	2,092	2,163	4,255	4,113
Distribution management
Disaggregation of Revenue [Line Items]
Revenues	702	710	2,061	1,798
Fund reimbursement revenue
Disaggregation of Revenue [Line Items]
Revenues	990	381	2,845	711
Incentive fees
Disaggregation of Revenue [Line Items]
Revenues	5,096	2,585	9,231	14,968
Specialized funds
Disaggregation of Revenue [Line Items]
Revenues	4,980	2,085	7,619	7,809
Customized separate accounts
Disaggregation of Revenue [Line Items]
Revenues	$ 116	$ 500	$ 1,612	$ 7,159