Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Unit [Abstract]
Net income – basic	$ 46,439	$ 58,160
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	26	145
Net income – diluted	$ 46,465	$ 58,305
Weighted average units outstanding – basic (in units)	95,144,000	96,987,000
Dilutive effect of compensatory options (in units)	72,000	336,000
Weighted average units outstanding – diluted (in units)	95,216,000	97,323,000
Basic net income per unit (in dollars per unit)	$ 0.49	$ 0.60
Diluted net income per unit (in dollars per unit)	$ 0.49	$ 0.60
Anti-dilutive units excluded from diluted net income computation (in units)	29,056	1,225,731