Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Equity in net income attributable to AB Unitholders		$ 101,415		$ 73,874		$ 63,201		$ 69,914		$ 87,909		$ 66,722		$ 59,023		$ 52,638		$ 308,404	$ 266,292	$ 270,647
Net income		$ 93,196		$ 66,999		$ 56,926		$ 62,259		$ 80,022		$ 59,828		$ 52,274		$ 46,439		$ 279,380	$ 238,563	$ 242,397
Basic net income per unit (in dollars per unit)		$ 0.97	[1]	$ 0.70	[1]	$ 0.59	[1]	$ 0.63	[1]	$ 0.84	[1]	$ 0.62	[1]	$ 0.54	[1]	$ 0.49	[1]	$ 2.88	$ 2.49	$ 2.50
Diluted net income per unit (in dollars per unit)		0.97	[1]	0.70	[1]	0.59	[1]	0.63	[1]	0.84	[1]	0.62	[1]	0.54	[1]	0.49	[1]	$ 2.88	$ 2.49	$ 2.50
Cash distributions per unit (in dollars per unit)	[2],[3]	$ 0.97		$ 0.69		$ 0.61		$ 0.64		$ 0.85		$ 0.63		$ 0.56		$ 0.49

[1] Basic and diluted net income per unit are computed independently for each of the periods presented. Accordingly, the sum of the quarterly net income per unit amounts may not agree to the total for the year.

[2] Cash distributions reflect the impact of AB’s non-GAAP adjustments.

[3] Declared and paid during the following quarter.