Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 204,400	$ 157,480	$ 593,172	$ 466,007
Other comprehensive income (loss):
Foreign currency translation adjustment, before reclassification and tax	(4,154)	7,735	(14,889)	24,091
Less: reclassification adjustment for losses included in net income upon liquidation	0	0	(100)	0
Foreign currency translation adjustments, before tax	(4,154)	7,735	(14,789)	24,091
Income tax benefit	0	0	0	0
Foreign currency translation adjustments, net of tax	(4,154)	7,735	(14,789)	24,091
Unrealized gains on investments:
Unrealized (losses) gains arising during period	0	(4)	0	6
Less: reclassification adjustment for gains included in net income	0	0	0	0
Change in unrealized (losses) gains on investments	0	(4)	0	6
Income tax benefit	0	5	0	3
Unrealized gains on investments, net of tax	0	1	0	9
Changes in employee benefit related items:
Amortization of prior service cost	6	6	17	18
Recognized actuarial gain	285	295	853	818
Changes in employee benefit related items	291	301	870	836
Income tax expense	(5)	(2)	(121)	(81)
Employee benefit related items, net of tax	286	299	749	755
Other	0	0	374	0
Other comprehensive (loss) income	(3,868)	8,035	(13,666)	24,855
Less: Comprehensive income in consolidated entities attributable to non-controlling interests	721	16,554	23,608	50,990
Comprehensive income attributable to AB Unitholders	$ 199,811	$ 148,961	$ 555,898	$ 439,872