Investment in AB (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 63,201	$ 59,023	133,115	$ 111,661
Changes in accumulated other comprehensive (loss) income	2,842	$ (1,112)	(4,635)	331
Cash distributions received from AB			(160,259)	(121,617)
Additional investments with proceeds from exercise of compensatory options to buy AB Holding Units			147	$ 8,951
Capital contributions (from) to AB			(971)
AB Holding Units retired			(46,178)
AB Holding Units issued to fund long-term incentive compensation plans			9,961
Change in AB Holding Units held by AB for long-term incentive compensation plans			1,234
Investment in AB as of June 30, 2020	$ 1,486,617		$ 1,486,617

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