Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									$ 3,430,316	$ 3,315,390	$ 3,156,149
Dividend and interest income, net of interest expense									47,216	45,827	45,997
Investment gains (losses)									38,659	2,653	92,102
Other revenues									2,241	3,491	4,273
Revenue Not Subject To Contract With Customer									88,116	51,971	142,372
Net revenues	$ 987,304	$ 877,867	$ 857,799	$ 795,462	$ 804,660	$ 850,176	$ 844,738	$ 867,787	3,518,432	3,367,361	3,298,521
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									2,372,429	2,244,068	2,106,525
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									99,615	118,143	94,780
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									407,911	439,432	449,919
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									291,999	254,477	245,367
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									80,268	87,166	94,972
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									82,776	76,919	71,724
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									77,394	75,974	75,024
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									$ 17,924	$ 19,211	$ 17,838