Valuation and Qualifying Account - Allowance for Doubtful Accounts (Details) - AllianceBernstein L.P. - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	$ 309	$ 395	$ 411
Credited to Costs and Expenses	100	132	0
Deductions	98	218	16	[1]
Balance at End of Period	$ 311	$ 309	$ 395

[1] Includes accounts written-off as uncollectible of $98.