Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									$ 3,315,390	$ 3,156,149	$ 2,892,144
Dividend and interest income, net of interest expense									45,827	45,997	37,816
Investment gains (losses)									2,653	92,102	93,353
Other revenues									3,491	4,273	5,466
Revenue Not Subject To Contract With Customer									51,971	142,372	136,635
Net revenues	$ 804,660	$ 850,176	$ 844,738	$ 867,787	$ 919,141	$ 812,150	$ 802,313	$ 764,917	3,367,361	3,298,521	3,028,779
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									2,244,068	2,106,525	1,900,719
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									118,143	94,780	32,752
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									439,432	449,919	479,875
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									254,477	245,367	197,766
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									87,166	94,972	114,641
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									76,919	71,724	71,998
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									75,974	75,024	77,690
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers									$ 19,211	$ 17,838	$ 16,703