Revenue Recognition - Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue Recognition
Total Revenues	$ 240,034	$ 270,154	$ 503,767	$ 529,564
Investment management fees
Revenue Recognition
Total Revenues	95,824	112,870	201,043	222,632
Funds
Revenue Recognition
Total Revenues	92,977	109,007	195,269	214,752
Institutional
Revenue Recognition
Total Revenues	2,847	3,863	5,774	7,880
Underwriting and distribution fees
Revenue Recognition
Total Revenues	123,633	133,495	260,576	259,740
Unaffiliated
Revenue Recognition
Total Revenues	14,134	17,191	29,996	34,191
Unaffiliated Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	13,670	16,615	28,946	33,081
Unaffiliated sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	373	493	824	935
Unaffiliated Other Revenues [Member]
Revenue Recognition
Total Revenues	91	83	226	175
Wealth Management
Revenue Recognition
Total Revenues	109,499	116,304	230,580	225,549
Wealth Management, Fee-based asset allocation product revenues
Revenue Recognition
Total Revenues	72,534	70,220	149,652	135,450
Wealth Management, Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	13,600	16,041	28,189	31,445
Wealth Management, sales commissions on other products
Revenue Recognition
Total Revenues	15,034	20,794	35,691	40,416
Wealth Management, other revenues
Revenue Recognition
Total Revenues	8,331	9,249	17,048	18,238
Shareholder service fees
Revenue Recognition
Total Revenues	$ 20,577	$ 23,789	$ 42,148	$ 47,192