Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue Streams [Abstract]
Revenue	$ 67,928	$ 69,567
Closed-end Funds [Member] | Performance-based [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member]
Revenue Streams [Abstract]
Revenue	$ 61,470	62,273
Advisory Fees [Member] | Performance-based [Member]
Revenue Streams [Abstract]
Revenue	$ 385	95
Advisory Fees [Member] | Conditional [Member]
Revenue Streams [Abstract]
Number of days for customer to make payment after being invoiced	60 days
Advisory Fees [Member] | Mutual Funds [Member]
Revenue Streams [Abstract]
Revenue	$ 23,472	23,556
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member] | Closed-end Funds [Member]
Revenue Streams [Abstract]
Revenue	$ 18,082	16,420
Number of days for customer to make payment after being invoiced	30 days
Advisory 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
Advisory Fees [Member] | Sub-advisory Accounts [Member]
Revenue Streams [Abstract]
Revenue	$ 616	732
Number of days for customer to make payment after being invoiced	30 days
Advisory Fees [Member] | Institutional & PWM [Member]
Revenue Streams [Abstract]
Revenue	$ 17,599	20,005
Number of days for customer to make payment after being invoiced	60 days
Advisory Fees [Member] | Institutional & PWM [Member] | Performance-based [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]
Revenue	$ 1,316	1,465
Number of days for customer to make payment after being invoiced	30 days
Distribution Fees and Other Income [Member]
Revenue Streams [Abstract]
Revenue	$ 6,458	$ 7,294
Number of days for customer to make payment after being invoiced	30 days