Investment in AB (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Change in Equity Method Investment [Roll Forward]
Investment in AB as of December 31, 2018			$ 1,490,701
Equity in net income attributable to AB Unitholders	$ 59,023	$ 65,388	111,661	$ 131,086
Changes in accumulated other comprehensive income (loss)	(1,112)	$ (7,205)	331	(3,857)
Additional investments with proceeds from exercise of compensatory options to buy AB Holding Units			8,951	8,314
Cash distributions received from AB			(121,617)	$ (167,861)
Capital contributions to AB			494
AB Holding Units retired			(73,383)
AB Holding Units issued to fund long-term incentive compensation plans			60,903
Change in AB Holding Units held by AB for long-term incentive compensation plans			(7,987)
Investment in AB as of June 30, 2019	$ 1,470,054		$ 1,470,054