Revenue Recognition (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) Fund	Mar. 31, 2021 USD ($)
Revenue Streams [Abstract]
Revenue	$ 69,623	$ 67,928
Performance-based [Member] | Minimum [Member]
Revenue Streams [Abstract]
Revenue	0
Investment Advisory and Incentive Fees [Member]
Revenue Streams [Abstract]
Revenue	63,762	61,470
Investment Advisory and Incentive Fees [Member] | Performance-based [Member]
Revenue Streams [Abstract]
Revenue	24	385
Investment Advisory and Incentive Fees [Member] | Open-end Funds [Member]
Revenue Streams [Abstract]
Revenue	23,352	23,472
Investment Advisory and Incentive Fees [Member] | Closed-end Funds [Member]
Revenue Streams [Abstract]
Revenue	19,075	18,082
Investment Advisory and Incentive Fees [Member] | Sub-advisory Accounts [Member]
Revenue Streams [Abstract]
Revenue	551	616
Investment Advisory and Incentive Fees [Member] | Institutional & Private Wealth Management [Member]
Revenue Streams [Abstract]
Revenue	18,622	17,599
Investment Advisory and Incentive Fees [Member] | SICAVs [Member]
Revenue Streams [Abstract]
Revenue	2,138	1,316
Advisory Fees [Member]
Revenue Streams [Abstract]
Revenue	$ 63,762	61,470
Advisory Fees [Member] | Conditional [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	60 days
Advisory Fees [Member] | Open-end Funds [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member] | Closed-end Funds [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member] | Sub-advisory Accounts [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member] | Institutional & Private Wealth Management [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	60 days
Advisory Fees [Member] | SICAVs [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member] | SICAVs [Member] | Performance-based [Member] | Non-US Closed-end Fund [Member]
Revenue Streams [Abstract]
Number of funds | Fund	1
Incentive Fees [Member] | Closed-end Funds [Member] | Performance-based [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Number of funds | Fund	2
Incentive Fees [Member] | SICAVs [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Distribution Fees and Other Income [Member]
Revenue Streams [Abstract]
Revenue	$ 5,861	$ 6,458
Number of days for customer to make payment after being invoiced	30 days