Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Unit [Abstract]
Net income – basic	$ 62,259	$ 46,439
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	15	26
Net income – diluted	$ 62,274	$ 46,465
Weighted average units outstanding – basic (in units)	98,309,000	95,144,000
Dilutive effect of compensatory options (in units)	32,000	72,000
Weighted average units outstanding – diluted (in units)	98,341,000	95,216,000
Basic net income per unit (in dollars per unit)	$ 0.63	$ 0.49
Diluted net income per unit (in dollars per unit)	$ 0.63	$ 0.49
Anti-dilutive units excluded from diluted net income computation (in units)	29,056	29,056