Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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)	36.40%	36.00%
Equity in net income attributable to AB Unitholders	$ 88,907	$ 69,914
Computation of income tax [Abstract]
AB qualifying revenues	$ 706,392	$ 702,340
Multiplied by: weighted average equity ownership interest for calculating tax (percent)	30.60%	30.60%
Multiplied by: federal tax (percent)	3.50%	3.50%
Federal income taxes	$ 7,572	$ 7,515
State income taxes	248	140
Total income taxes	$ 7,820	$ 7,655
Effective tax rate (percent)	8.80%	10.90%
Changes in components for calculation of income tax [Abstract]
Change in net income attributable to AllianceBernstein Unitholders (percent)	25.60%
Change in equity in net income attributable to AllianceBernstein Unitholders (percent)	27.20%
Change in AllianceBernstein qualifying revenues (percent)	0.60%
Change in income taxes (percent)	2.20%
Variable Interest Entity, Primary Beneficiary
Income Tax Contingency [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 244,131	$ 194,320