Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of net (loss) income per unit [Abstract]
Net income – basic	$ 42,687	$ 44,134	$ 136,496	$ 123,147
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	301	409	1,083	1,085
Net income – diluted	$ 42,988	$ 44,543	$ 137,579	$ 124,232
Weighted average units outstanding – basic	99,651,000	97,070,000	100,255,000	96,549,000
Dilutive effect of compensatory options	970,000	1,249,000	1,113,000	1,174,000
Weighted average units outstanding – diluted	100,621,000	98,319,000	101,368,000	97,723,000
Basic net income per unit (in dollars per unit)	$ 0.43	$ 0.45	$ 1.36	$ 1.28
Diluted net income per unit (in dollars per unit)	$ 0.43	$ 0.45	$ 1.36	$ 1.27
Anti-dilutive units excluded from diluted net income computation	2,771,250	2,774,117	2,383,589	2,806,033