Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Total amount of AB Holding Units Purchased (in units)	1,000,000.0	900,000
Total Cash Paid for AB Holding Units Purchased	$ 37,400	$ 19,800
Open Market Purchases of AB Holding Units (in units)	600,000	800,000
Total Cash Paid for Open Market Purchases of AB Holding Units	$ 24,200	$ 17,300
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued upon options exercised (in units)	100,000	5,182
Proceeds from stock options exercised	$ 1,914	$ 147
Employees and Eligible Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted AB Holding Unit awards granted to employees and Eligible Directors (in units)	3,400,000	100,000