Related Party Transactions - Revenues for Services Provided (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Investment advisory and services fees	$ 2,200,400	$ 1,933,471	$ 1,973,837
Distribution revenues	412,063	384,405	427,156
Other revenues	98,040	99,859	101,169
Bernstein research services	449,919	479,875	493,463
Mutual Funds [Member]
Related Party Transaction [Line Items]
Investment advisory and services fees	1,148,467	998,892	1,056,227
Distribution revenues	397,674	371,604	415,380
Shareholder servicing fees	73,310	76,201	85,207
Other revenues	6,942	6,253	4,939
Bernstein research services	$ 13	$ 5	$ 4