Investment in AB (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Change in Equity Method Investment [Roll Forward]
Investment in AB as of December 31, 2019			$ 1,554,203
Equity in net income attributable to AB Unitholders	$ 73,874	$ 66,722	206,989	$ 178,383
Changes in accumulated other comprehensive income	6,061	$ (4,126)	1,426	(3,795)
Cash distributions received from AB			(225,802)	(182,475)
Additional investments with proceeds from exercise of compensatory options to buy AB Holding Units			147	$ 9,642
Capital contributions (from) AB			(865)
AB Holding Units retired			(54,823)
AB Holding Units issued to fund long-term incentive compensation plans			10,243
Change in AB Holding Units held by AB for long-term incentive compensation plans			4,745
Investment in AB as of September 30, 2020	$ 1,496,263		$ 1,496,263