Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Total amount of AB Holding Units Purchased (in units)	300,000	900,000	2,500,000	2,900,000
Total Cash Paid for AB Holding Units Purchased	$ 6,800	$ 25,100	$ 54,400	$ 83,700
Open Market Purchases of AB Holding Units (in units)	200,000	600,000	2,400,000	2,500,000
Total Cash Paid for Open Market Purchases of AB Holding Units	$ 6,700	$ 15,300	$ 51,800	$ 70,600
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued upon options exercised (in units)			5,182	400,000
Proceeds from stock options exercised			$ 147	$ 9,642
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)			500,000	1,900,000