Revenue Recognition - Disaggregation of revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue Recognition
Total Revenues	$ 1,070,315	$ 1,160,301	$ 1,157,144
Investment management fees
Revenue Recognition
Total Revenues	445,144	507,906	531,850
Investment management fees - Funds
Revenue Recognition
Total Revenues	430,028	486,181	506,868
Investment management fees - Institutional
Revenue Recognition
Total Revenues	15,116	21,725	24,982
Underwriting and distribution fees
Revenue Recognition
Total Revenues	531,836	550,010	518,699
Unaffiliated
Revenue Recognition
Total Revenues	67,247	80,495	93,993
Unaffiliated Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	65,227	78,041	91,313
Unaffiliated sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	1,730	1,886	1,498
Unaffiliated other revenues
Revenue Recognition
Total Revenues	290	568	1,182
Broker-dealer
Revenue Recognition
Total Revenues	464,589	469,515	424,706
Broker-dealer fee based asset allocation product revenue
Revenue Recognition
Total Revenues	284,188	269,069	240,089
Broker-dealer Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	63,197	70,938	75,850
Broker-dealer sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	48,471	54,895	55,293
Broker-dealer sales commissions on other products
Revenue Recognition
Total Revenues	32,314	36,131	31,286
Broker-dealer other revenues
Revenue Recognition
Total Revenues	36,419	38,482	22,188
Shareholder service fees
Revenue Recognition
Total Revenues	$ 93,335	$ 102,385	$ 106,595