Investment in AB (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 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	52,638	$ 65,698
Changes in accumulated other comprehensive income (loss)	1,443	3,348
Additional investments with proceeds from exercise of compensatory options to buy AB Holding Units	7,382	4,008
Cash distributions received from AB	(67,485)	(88,671)
Capital contributions from AB	(931)	$ (1,696)
AB Holding Units retired	(69,653)
AB Holding Units issued to fund long-term incentive compensation plans	11,313
Change in AB Holding Units held by AB for long-term incentive compensation plans	3,295
Investment in AB as of March 31, 2019	$ 1,428,703