Investment in AB (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 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	69,914	$ 52,638
Changes in accumulated other comprehensive (loss) income	(7,477)	1,443
Cash distributions received from AB	(91,562)	(67,485)
Additional investments with proceeds from exercise of compensatory options to buy AB Holding Units	147	7,382
Capital contributions (from) to AB	(699)	$ (931)
AB Holding Units retired	(14,220)
AB Holding Units issued to fund long-term incentive compensation plans	8,458
Change in AB Holding Units held by AB for long-term incentive compensation plans	(1,566)
Investment in AB as of March 31, 2020	$ 1,517,198

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