Revenue Recognition (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Fund	Sep. 30, 2020 USD ($)
Revenue Streams [Abstract]
Revenue	$ 75,907	$ 61,252	$ 219,459	$ 188,378
Performance-based [Member] | Minimum [Member]
Revenue Streams [Abstract]
Revenue			$ 0
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
Advisory Fees [Member]
Revenue Streams [Abstract]
Revenue	69,147	54,894	$ 199,502	168,637
Advisory Fees [Member] | Performance-based [Member]
Revenue Streams [Abstract]
Revenue	63	62	$ 3,955	405
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	25,075	22,163	$ 73,256	66,084
Number of days for customer to make payment after being invoiced			30 days
Advisory Fees [Member] | Closed-end Funds [Member]
Revenue Streams [Abstract]
Revenue	22,298	16,218	$ 60,185	47,232
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	636	521	$ 1,902	1,770
Number of days for customer to make payment after being invoiced			30 days
Advisory Fees [Member] | Institutional & PWM [Member]
Revenue Streams [Abstract]
Revenue	19,246	14,771	$ 55,437	49,319
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	1,829	1,159	$ 4,767	3,827
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
Distribution Fees and Other Income [Member]
Revenue Streams [Abstract]
Revenue	$ 6,760	$ 6,358	$ 19,957	$ 19,741
Number of days for customer to make payment after being invoiced			30 days