Revenue Recognition - Disaggregation of revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue Recognition
Total Revenues	$ 1,160,301	$ 1,157,144	$ 1,239,023
Investment management fees
Revenue Recognition
Total Revenues	507,906	531,850	557,112
Investment management fees - Funds
Revenue Recognition
Total Revenues	486,181	506,868	521,207
Investment management fees - Institutional
Revenue Recognition
Total Revenues	21,725	24,982	35,905
Underwriting and distribution fees
Revenue Recognition
Total Revenues	550,010	518,699	561,670
Unaffiliated
Revenue Recognition
Total Revenues	80,495	93,993	125,415
Unaffiliated Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	78,041	91,313	121,926
Unaffiliated sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	1,886	1,498	565
Unaffiliated other revenues
Revenue Recognition
Total Revenues	568	1,182	2,924
Broker-dealer
Revenue Recognition
Total Revenues	469,515	424,706	436,255
Broker-dealer fee based asset allocation product revenue
Revenue Recognition
Total Revenues	269,069	240,089	224,319
Broker-dealer Rule 12b-1 service and distribution fees
Revenue Recognition
Total Revenues	70,938	75,850	93,260
Broker-dealer sales commissions on front-end load mutual fund and variable annuity sales
Revenue Recognition
Total Revenues	54,895	55,293	67,169
Broker-dealer sales commissions on other products
Revenue Recognition
Total Revenues	36,131	31,286	31,246
Broker-dealer other revenues
Revenue Recognition
Total Revenues	38,482	22,188	20,261
Shareholder service fees
Revenue Recognition
Total Revenues	$ 102,385	$ 106,595	$ 120,241