Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 832,568	$ 763,325	$ 1,653,728	$ 1,492,826
Dividend and interest income, net of interest expense	9,062	13,153	27,737	22,919
Investment gains (losses)	213	24,113	26,295	49,314
Other revenues	2,895	1,722	4,765	2,171
Revenue not subject to contract with customer	12,170	38,988	58,797	74,404
Net revenues	844,738	802,313	1,712,525	1,567,230
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	561,572	516,485	1,128,910	1,008,661
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	35,298	14,678	41,558	20,792
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	106,211	109,470	220,611	222,211
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	64,329	58,624	131,077	113,143
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	22,075	23,688	44,609	48,478
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	18,714	17,837	37,436	35,082
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	18,985	18,549	38,515	36,513
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 5,384	$ 3,994	$ 11,012	$ 7,946