Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 779,498	$ 720,800	$ 694,846
Other comprehensive (loss) income:
Foreign currency translation adjustments, before reclassification and tax:	(19,337)	28,123	(19,849)
Less: reclassification adjustment for losses included in net income upon liquidation	(100)	0	(6)
Foreign currency translation adjustments, before tax	(19,237)	28,123	(19,843)
Income tax expense	620	0	0
Foreign currency translation adjustments, net of tax	(18,617)	28,123	(19,843)
Unrealized gains on investments:
Unrealized gains arising during period	0	6	10
Less: reclassification adjustment for losses included in net income	0	0	(6)
Changes in unrealized gains on investments	0	6	16
Income tax benefit (expense)	0	3	(7)
Unrealized gains on investments, net of tax	0	9	9
Changes in employee benefit related items:
Amortization of prior service cost	24	24	93
Recognized actuarial gain (loss)	1,586	(3,190)	(3,043)
Changes in employee benefit related items	1,610	(3,166)	(2,950)
Income tax expense	(139)	(27)	(22)
Employee benefit related items, net of tax	1,471	(3,193)	(2,972)
Other	374	0	0
Other comprehensive (loss) gain	(16,772)	24,939	(22,806)
Less: Comprehensive income in consolidated entities attributable to non-controlling interests	21,864	59,379	21,426
Comprehensive income attributable to AB Unitholders	$ 740,862	$ 686,360	$ 650,614