Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Unit [Abstract]
Net income – basic	$ 52,274	$ 58,457	$ 98,713	$ 116,617
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	19	115	45	259
Net income – diluted	$ 52,293	$ 58,572	$ 98,758	$ 116,876
Weighted average units outstanding – basic (in units)	96,283,000	98,368,000	95,717,000	97,673,000
Dilutive effect of compensatory options (in units)	48,000	272,000	60,000	303,000
Weighted average units outstanding – diluted (in units)	96,331,000	98,640,000	95,777,000	97,976,000
Basic net income per unit (in dollars per unit)	$ 0.54	$ 0.59	$ 1.03	$ 1.19
Diluted net income per unit (in dollars per unit)	$ 0.54	$ 0.59	$ 1.03	$ 1.19
Anti-dilutive units excluded from diluted net income computation (in units)	29,056	850,155	29,056	1,211,906