Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 821,160	$ 729,501
Dividend and interest income, net of interest expense	18,675	9,766
Investment gains (losses)	26,082	25,201
Other Revenue, Net	1,870	449
Revenue not subject to contract with customer	46,627	35,416
Net revenues	867,787	764,917
Base fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	567,338	492,176
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	6,260	6,114
Bernstein research services
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	114,400	112,741
All-in-management fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	66,748	54,519
12b-1 fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	22,534	24,789
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	18,722	17,246
Shareholder servicing fees
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	19,530	17,964
Other
Disaggregation of Revenue [Line Items]
Revenue subject to contracts with customers	$ 5,628	$ 3,952