Revenue Recognition - Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition
Total Revenues	$ 295,118	$ 289,447	$ 888,071	$ 862,668
Investment management fees
Revenue Recognition
Total Revenues	129,302	134,149	393,385	395,463
Investment management fees - Funds
Revenue Recognition
Total Revenues	123,764	128,078	376,193	376,563
Investment management fees - Institutional
Revenue Recognition
Total Revenues	5,538	6,071	17,192	18,900
Underwriting and distribution fees
Revenue Recognition
Total Revenues	140,308	128,892	416,222	386,499
Unaffiliated
Revenue Recognition
Total Revenues	20,274	22,892	62,611	71,305
Unaffiliated Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	19,707	22,322	60,734	69,191
Unaffiliated sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	441	353	1,418	1,118
Unaffiliated other revenues
Revenue Recognition
Total Revenues	126	217	459	996
Broker-dealer
Revenue Recognition
Total Revenues	120,034	106,000	353,611	315,194
Broker-dealer fee based asset allocation product revenue
Revenue Recognition
Total Revenues	69,468	61,115	201,565	176,184
Broker-dealer Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	18,106	19,026	54,591	56,544
Broker-dealer sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	13,651	12,941	41,900	41,796
Broker-dealer sales commissions on other products
Revenue Recognition
Total Revenues	9,111	7,974	26,632	23,671
Broker-dealer other revenues
Revenue Recognition
Total Revenues	9,698	4,944	28,923	16,999
Shareholder service fees
Revenue Recognition
Total Revenues	$ 25,508	$ 26,406	$ 78,464	$ 80,706