Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Unit [Abstract]
Net income – basic	$ 56,926	$ 52,274	$ 119,185	$ 98,713
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options	3	19	18	45
Net income – diluted	$ 56,929	$ 52,293	$ 119,203	$ 98,758
Weighted average units outstanding – basic (in units)	96,892,000	96,283,000	96,526,000	95,717,000
Dilutive effect of compensatory options (in units)	10,000	48,000	22,000	60,000
Weighted average units outstanding – diluted (in units)	96,902,000	96,331,000	96,548,000	95,777,000
Basic net income per unit (in dollars per unit)	$ 0.59	$ 0.54	$ 1.23	$ 1.03
Diluted net income per unit (in dollars per unit)	$ 0.59	$ 0.54	$ 1.23	$ 1.03
Anti-dilutive units excluded from diluted net income computation (in units)	44,877	29,056	44,877	29,056