Consolidated Company-Sponsored Investment Funds (Summary of Balance Sheet Amounts) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 652,451	$ 998,448	$ 963,168	$ 994,510
Other assets	281,424	211,893
Total assets	8,672,114	9,295,167
Liabilities	4,589,032	4,630,276
Redeemable non-controlling interest	108,524	601,587
Partners' capital attributable to AB Unitholders	3,972,899	4,061,740
Non-redeemable non-controlling interests in consolidated entities	1,659	1,564
Total liabilities, redeemable non-controlling interest and capital	8,672,114	9,295,167
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	23,693	326,518
Investments	301,625	1,246,283
Other assets	8,178	35,397
Liabilities	6,972	698,101
Redeemable non-controlling interest	103,160	596,223
Non-redeemable non-controlling interests in consolidated entities	704	757
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	23,693	326,518
Investments	301,625	1,246,283
Other assets	8,178	35,397
Total assets	333,496	1,608,198
Liabilities	6,972	698,101
Redeemable non-controlling interest	103,160	596,223
Partners' capital attributable to AB Unitholders	222,660	313,117
Non-redeemable non-controlling interests in consolidated entities	704	757
Total liabilities, redeemable non-controlling interest and capital	333,496	1,608,198
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	22,881	326,158
Investments	196,391	1,189,835
Other assets	6,109	33,931
Total assets	225,381	1,549,924
Liabilities	5,141	695,997
Redeemable non-controlling interest	92,730	596,241
Partners' capital attributable to AB Unitholders	126,806	256,929
Non-redeemable non-controlling interests in consolidated entities	704	757
Total liabilities, redeemable non-controlling interest and capital	225,381	1,549,924
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	812	360
Investments	105,234	56,448
Other assets	2,069	1,466
Total assets	108,115	58,274
Liabilities	1,831	2,104
Redeemable non-controlling interest	10,430	(18)
Partners' capital attributable to AB Unitholders	95,854	56,188
Non-redeemable non-controlling interests in consolidated entities	0	0
Total liabilities, redeemable non-controlling interest and capital	$ 108,115	$ 58,274