Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 206,846	$ 156,255
Other comprehensive income (loss):
Foreign currency translation adjustments, before tax	9,921	9,001
Income tax benefit	0	(134)
Foreign currency translation adjustments, net of tax	9,921	8,867
Unrealized (losses) on investments:
Unrealized (losses) arising during period	0	(16)
Less: reclassification adjustment for (losses) included in net income	0	0
Change in unrealized (losses) on investments	0	(16)
Income tax benefit (expense)	0	(2)
Unrealized (losses) on investments, net of tax	0	(18)
Changes in employee benefit related items:
Amortization of prior service cost	6	6
Recognized actuarial gain	282	259
Changes in employee benefit related items	288	265
Income tax (expense)	(118)	(76)
Employee benefit related items, net of tax	170	189
Other comprehensive income	10,091	9,038
Less: Comprehensive income in consolidated entities attributable to non-controlling interests	22,667	16,394
Comprehensive income attributable to AB Unitholders	$ 194,270	$ 148,899