Consolidated Company-Sponsored Investment Funds (Summary of Balance Sheet Amounts) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 257,718	$ 297,940
Total assets	8,858,838	8,789,098
Liabilities	4,856,208	4,724,080
Redeemable non-controlling interest	158,873	148,809
Partners' capital attributable to AB Unitholders	3,842,812	3,915,260
Total liabilities, redeemable non-controlling interest and capital	8,858,838	8,789,098
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	7,767	13,118
Investments	385,309	351,696
Other assets	26,190	22,840
Liabilities	29,648	22,610
Redeemable non-controlling interest	155,985	145,921
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	7,767	13,118
Investments	385,309	351,696
Other assets	26,190	22,840
Total assets	419,266	387,654
Liabilities	29,648	22,610
Redeemable non-controlling interest	155,985	145,921
Partners' capital attributable to AB Unitholders	233,633	219,123
Total liabilities, redeemable non-controlling interest and capital	419,266	387,654
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	5,948	11,880
Investments	230,755	217,840
Other assets	12,668	6,024
Total assets	249,371	235,744
Liabilities	14,050	5,215
Redeemable non-controlling interest	116,343	117,523
Partners' capital attributable to AB Unitholders	118,978	113,006
Total liabilities, redeemable non-controlling interest and capital	249,371	235,744
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	1,819	1,238
Investments	154,554	133,856
Other assets	13,522	16,816
Total assets	169,895	151,910
Liabilities	15,598	17,395
Redeemable non-controlling interest	39,642	28,398
Partners' capital attributable to AB Unitholders	114,655	106,117
Total liabilities, redeemable non-controlling interest and capital	$ 169,895	$ 151,910