Consolidated Company-Sponsored Investment Funds (Summary of Balance Sheet Amounts) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,220,555	$ 998,448	$ 1,064,877	$ 994,510
Other assets	236,727	211,893
Total assets	10,561,530	9,295,167
Liabilities	5,507,089	4,630,276
Redeemable non-controlling interest	996,966	601,587
Partners' capital attributable to AB Unitholders	4,055,845	4,061,740
Non-redeemable non-controlling interests in consolidated entities	1,630	1,564
Total liabilities, redeemable non-controlling interest and capital	10,561,530	9,295,167
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	580,721	326,518
Investments	1,956,470	1,246,283
Other assets	44,492	35,397
Liabilities	1,222,874	698,101
Redeemable non-controlling interest	991,602	596,223
Non-redeemable non-controlling interests in consolidated entities	710	757
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	580,721	326,518
Investments	1,956,470	1,246,283
Other assets	44,492	35,397
Total assets	2,581,683	1,608,198
Liabilities	1,222,874	698,101
Redeemable non-controlling interest	991,602	596,223
Partners' capital attributable to AB Unitholders	366,497	313,117
Non-redeemable non-controlling interests in consolidated entities	710	757
Total liabilities, redeemable non-controlling interest and capital	2,581,683	1,608,198
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	580,239	326,158
Investments	1,826,576	1,189,835
Other assets	40,242	33,931
Total assets	2,447,057	1,549,924
Liabilities	1,218,612	695,997
Redeemable non-controlling interest	981,961	596,241
Partners' capital attributable to AB Unitholders	245,774	256,929
Non-redeemable non-controlling interests in consolidated entities	710	757
Total liabilities, redeemable non-controlling interest and capital	2,447,057	1,549,924
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	482	360
Investments	129,894	56,448
Other assets	4,250	1,466
Total assets	134,626	58,274
Liabilities	4,262	2,104
Redeemable non-controlling interest	9,641	(18)
Partners' capital attributable to AB Unitholders	120,723	56,188
Non-redeemable non-controlling interests in consolidated entities	0	0
Total liabilities, redeemable non-controlling interest and capital	$ 134,626	$ 58,274