Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Payment Arrangement [Abstract]
Total amount of AB Holding Units Purchased (in units)	1,300,000	0	2,200,000	2,000,000.0
Total Cash Paid for AB Holding Units Purchased	$ 27,800	$ 0	$ 47,600	$ 58,600
Open Market Purchases of AB Holding Units (in units)	1,300,000	0	2,200,000	1,900,000
Total Cash Paid for Open Market Purchases of AB Holding Units	$ 27,800	$ 0	$ 45,100	$ 55,200
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	$ 8,951
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)			200,000	1,700,000