Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
New York City unincorporated business tax (percent)			4.00%
Federal tax rate on partnership gross income (percent)			3.50%
Income Tax Contingency [Line Items]
Multiplied by: weighted average equity ownership interest (percent)	35.50%	35.50%	35.70%	35.50%
Equity in net income attributable to AB Unitholders	$ 73,874	$ 66,722	$ 206,989	$ 178,383
Computation of income tax [Abstract]
AB qualifying revenues	$ 642,303	$ 656,173	$ 1,931,252	$ 1,886,176
Multiplied by: weighted average equity ownership interest for calculating tax (percent)	30.00%	29.40%	30.20%	29.50%
Multiplied by: federal tax (percent)	3.50%	3.50%	3.50%	3.50%
Federal income taxes	$ 6,738	$ 6,759	$ 20,432	$ 19,459
State income taxes	137	135	373	383
Total income taxes	$ 6,875	$ 6,894	$ 20,805	$ 19,842
Effective tax rate (percent)	9.30%	10.30%	10.10%	11.10%
Changes in components for calculation of income tax [Abstract]
Change in net income attributable to AllianceBernstein Unitholders (percent)	10.70%		15.20%
Change in equity in net income attributable to AllianceBernstein Unitholders (percent)	10.70%		16.00%
Change in AllianceBernstein qualifying revenues (percent)	(2.10%)		2.40%
Change in income taxes (percent)	(0.30%)		4.90%
Variable Interest Entity, Primary Beneficiary
Income Tax Contingency [Line Items]
Net income attributable to AB Unitholders	$ 207,976	$ 187,811	$ 579,617	$ 503,177