Related Party Transactions - Revenues for Services Provided (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	$ 3,315,390	$ 3,156,149	$ 2,892,144
Other revenues	98,676	97,135	99,859
Mutual Funds
Related Party Transaction [Line Items]
Other revenues	7,262	6,942	6,253
Investment advisory and services fees
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	2,362,211	2,201,305	1,933,471
Investment advisory and services fees | Mutual Funds
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	1,207,086	1,148,467	998,892
Distribution revenues
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	418,562	412,063	384,405
Distribution revenues | Mutual Funds
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	403,965	397,674	371,604
Shareholder servicing fees
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	75,974	75,024	77,690
Shareholder servicing fees | Mutual Funds
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	74,019	73,310	76,201
Bernstein research services
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	439,432	449,919	479,875
Bernstein research services | Mutual Funds
Related Party Transaction [Line Items]
Revenue subject to contracts with customers	$ 33	$ 13	$ 5