Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 834,761	$ 834,203	$ 1,603,947	$ 1,656,006
Dividend and interest income, net of interest expense	11,352	9,062	21,535	27,737
Investment gains (losses)	10,949	213	26,684	26,295
Other revenues	737	1,260	1,095	2,487
Revenue not subject to contract with customer	23,038	10,535	49,314	56,519
Net revenues	857,799	844,738	1,653,261	1,712,525
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	585,077	562,810	1,137,307	1,130,666
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	11,287	35,298	15,651	41,558
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	105,991	106,211	196,226	220,611
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	68,494	64,329	130,267	131,077
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	20,182	22,075	39,768	44,609
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	19,671	18,714	38,821	37,436
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	19,563	18,985	37,393	38,515
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 4,496	$ 5,781	$ 8,514	$ 11,534