Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Unit [Abstract]
Net income – basic	$ 81,087	$ 62,259
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	18	15
Net income – diluted	$ 81,105	$ 62,274
Weighted average units outstanding – basic (in units)	100,146,000	98,309,000
Dilutive effect of compensatory options (in units)	32,000	32,000
Weighted average units outstanding – diluted (in units)	100,178,000	98,341,000
Basic net income per unit (in dollars per unit)	$ 0.81	$ 0.63
Diluted net income per unit (in dollars per unit)	$ 0.81	$ 0.63
Anti-dilutive units excluded from diluted net income (in units)	0	29,056