Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 979,234	$ 603,896	$ 563,246
Investment management fees
Disaggregation of Revenue [Line Items]
Revenues	781,585	505,338	461,477
Open-end funds
Disaggregation of Revenue [Line Items]
Revenues	393,673	247,519	229,637
Closed-end funds
Disaggregation of Revenue [Line Items]
Revenues	63,301	36,833	42,199
Retail separate accounts
Disaggregation of Revenue [Line Items]
Revenues	174,919	104,932	82,999
Institutional accounts
Disaggregation of Revenue [Line Items]
Revenues	143,487	109,531	96,429
Structured products
Disaggregation of Revenue [Line Items]
Revenues	4,726	4,012	6,381
Other products
Disaggregation of Revenue [Line Items]
Revenues	$ 1,479	$ 2,511	$ 3,832