Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenue	$ 489,637	$ 566,906	$ 583,832
North America
Disaggregation of Revenue [Line Items]
Total revenue	423,129	496,368	506,364
Japan
Disaggregation of Revenue [Line Items]
Total revenue	31,869	36,056	38,039
Asia Pacific, excluding Japan
Disaggregation of Revenue [Line Items]
Total revenue	13,221	13,043	13,099
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	21,418	21,439	26,330
Open-end funds
Disaggregation of Revenue [Line Items]
Total revenue	269,727	326,172	328,647
Institutional accounts
Disaggregation of Revenue [Line Items]
Total revenue	123,565	134,012	146,345
Closed-end funds
Disaggregation of Revenue [Line Items]
Total revenue	$ 96,345	$ 106,722	$ 108,840