Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Unit [Abstract]
Net income – basic	$ 58,457	$ 41,741	$ 116,617	$ 85,651
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	115	137	259	313
Net income – diluted	$ 58,572	$ 41,878	$ 116,876	$ 85,964
Weighted average units outstanding – basic (in units)	98,368,000	96,061,000	97,673,000	96,150,000
Dilutive effect of compensatory options (in units)	272,000	430,000	303,000	482,000
Weighted average units outstanding – diluted (in units)	98,640,000	96,491,000	97,976,000	96,632,000
Basic net income per unit (in dollars per unit)	$ 0.59	$ 0.43	$ 1.19	$ 0.89
Diluted net income per unit (in dollars per unit)	$ 0.59	$ 0.43	$ 1.19	$ 0.89
Anti-dilutive units excluded from diluted net income computation (in units)	850,155	2,507,179	1,211,906	2,452,633