Related Party Transactions (Details) - Affiliated Entity - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transactions Revenue [Abstract]
Investment advisory and administrative fees	$ 264,116,000	$ 241,255,000	$ 236,832,000
Distribution and service fees	30,048,000	29,090,000	30,747,000
Total	294,164,000	270,345,000	267,579,000
Related Party Transactions Summary [Abstract]
Proceeds from sales	37,326,000	10,872,000	15,105,000
Gross realized gains	241,000	28,000	80,000
Gross realized losses, including other-than-temporary impairment	(907,000)	(4,448,000)	0
Dividend income	52,000	481,000	675,000
Fund expenses, included in general and administrative expenses	11,100,000	8,600,000	$ 8,700,000
Receivables, Company sponsored mutual funds	27,725,000	22,560,000
Accounts Payable, Company sponsored mutual funds	$ 1,498,000	$ 845,000