Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 720,800	$ 694,846	$ 586,302
Other comprehensive (loss) income:
Foreign currency translation adjustments, before reclassification and tax:	28,123	(19,849)	(15,396)
Less: reclassification adjustment for (losses) gains included in net income upon liquidation	0	(6)	1,542
Foreign currency translation adjustments, before tax	28,123	(19,843)	(16,938)
Income tax expense	0	0	0
Foreign currency translation adjustments, net of tax	28,123	(19,843)	(16,938)
Unrealized gains (losses) on investments:
Unrealized gains (losses) arising during period	6	10	(357)
Less: reclassification adjustment for (losses) gains included in net income	0	(6)	1,256
Changes in unrealized gains (losses) on investments	6	16	(1,613)
Income tax benefit (expense)	3	(7)	701
Unrealized gains (losses) on investments, net of tax	9	9	(912)
Changes in employee benefit related items:
Amortization of prior service cost	24	93	(895)
Recognized actuarial (loss) gain	(3,190)	(3,043)	3,267
Changes in employee benefit related items	(3,166)	(2,950)	2,372
Income tax expense	(27)	(22)	(165)
Employee benefit related items, net of tax	(3,193)	(2,972)	2,207
Other comprehensive gain (loss)	24,939	(22,806)	(15,643)
Less: Comprehensive income in consolidated entities attributable to non-controlling interests	59,379	21,426	6,242
Comprehensive income attributable to AB Unitholders	$ 686,360	$ 650,614	$ 564,417