Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 837,395	$ 834,761	$ 1,744,715	$ 1,603,947
Not subject to contracts with customers:
Dividend and interest income, net of interest expense	9,257	11,352	20,403	21,535
Investment gains (losses)	24,189	10,949	(20,117)	26,684
Other revenues	608	737	604	1,095
Total revenue not from contract with customer	34,054	23,038	890	49,314
Net revenues	871,449	857,799	1,745,605	1,653,261
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	569,296	585,077	1,182,883	1,137,307
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	8,907	11,287	17,045	15,651
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	113,609	105,991	242,832	196,226
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	75,828	68,494	162,185	130,267
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	17,830	20,182	37,283	39,768
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	26,441	19,671	51,488	38,821
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	19,694	19,563	40,537	37,393
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 5,790	$ 4,496	$ 10,462	$ 8,514