Consolidated Company-Sponsored Investment Funds (Summary of Balance Sheet Amounts) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 311,836	$ 297,940
Total assets	8,794,006	8,789,098
Liabilities	4,704,231	4,724,080
Redeemable non-controlling interest	215,634	148,809
Partners' capital attributable to AB Unitholders	3,873,121	3,915,260
Total liabilities, redeemable non-controlling interest and capital	8,794,006	8,789,098
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	10,665	13,118
Investments	470,435	351,696
Other assets	28,619	22,840
Liabilities	35,583	22,610
Redeemable non-controlling interest	212,746	145,921
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	10,665	13,118
Investments	470,435	351,696
Other assets	28,619	22,840
Total assets	509,719	387,654
Liabilities	35,583	22,610
Redeemable non-controlling interest	212,746	145,921
Partners' capital attributable to AB Unitholders	261,390	219,123
Total liabilities, redeemable non-controlling interest and capital	509,719	387,654
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	8,915	11,880
Investments	304,067	217,840
Other assets	14,450	6,024
Total assets	327,432	235,744
Liabilities	17,536	5,215
Redeemable non-controlling interest	166,285	117,523
Partners' capital attributable to AB Unitholders	143,611	113,006
Total liabilities, redeemable non-controlling interest and capital	327,432	235,744
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	1,750	1,238
Investments	166,368	133,856
Other assets	14,169	16,816
Total assets	182,287	151,910
Liabilities	18,047	17,395
Redeemable non-controlling interest	46,461	28,398
Partners' capital attributable to AB Unitholders	117,779	106,117
Total liabilities, redeemable non-controlling interest and capital	$ 182,287	$ 151,910