Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Unit [Abstract]
Net income – basic	$ 43,178	$ 50,258	$ 128,829	$ 143,922
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	136	221	450	581
Net income – diluted	$ 43,314	$ 50,479	$ 129,279	$ 144,503
Weighted average units outstanding – basic (in units)	93,374,000	95,890,000	95,218,000	97,643,000
Dilutive effect of compensatory options (in units)	400,000	590,000	455,000	554,000
Weighted average units outstanding – diluted (in units)	93,774,000	96,480,000	95,673,000	98,197,000
Basic net income per unit (in dollars per unit)	$ 0.46	$ 0.52	$ 1.35	$ 1.47
Diluted net income per unit (in dollars per unit)	$ 0.46	$ 0.52	$ 1.35	$ 1.47
Anti-dilutive units excluded from diluted net income computation (in units)	2,427,527	2,873,106	2,427,527	2,873,106