Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 769,186	$ 821,803
Dividend and interest income, net of interest expense	10,183	18,675
Investment gains (losses)	15,735	26,082
Other revenues	358	1,227
Revenue not subject to contract with customer	26,276	45,984
Net revenues	795,462	867,787
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	552,230	567,856
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	4,364	6,260
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	90,235	114,400
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	61,773	66,748
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	19,586	22,534
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	19,150	18,722
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	17,830	19,530
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 4,018	$ 5,753

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Amount of realized and unrealized gain (loss), from the firm's direct investment activity, conducted separately from customer trading activities, and includes, but is not limited to, investments in private equity, alternative investment products, real estate, and exchanges and memberships.

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