Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 861,148	$ 841,442	$ 2,465,095	$ 2,497,449
Dividend and interest income, net of interest expense	11,904	7,467	33,439	35,204
Investment gains (losses)	4,433	565	31,117	26,860
Other revenues	382	702	1,477	3,188
Revenue not subject to contract with customer	16,719	8,734	66,033	65,252
Net revenues	877,867	850,176	2,531,128	2,562,701
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	608,765	568,918	1,746,072	1,699,584
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	7,619	41,145	23,270	82,703
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	102,014	103,581	298,240	324,192
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	77,110	62,807	207,377	193,884
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	20,287	22,136	60,055	66,746
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	21,238	19,545	60,059	56,980
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	20,020	19,017	57,413	57,533
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 4,095	$ 4,293	$ 12,609	$ 15,827