Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
AB Holding Units purchased (in units)	900,000	1,600,000	2,900,000	2,900,000
Amount paid for AB Holding Units acquired	$ 25,100	$ 48,000	$ 83,700	$ 83,200
Open-market purchases of AB Holding Units (in units)	600,000	1,600,000	2,500,000	2,800,000
Amount paid for open-market purchases of AB Holding Units	$ 15,300	$ 48,000	$ 70,600	$ 80,900
Units granted to employees and Eligible Directors (in units)			1,900,000	2,500,000
Units issued upon exercise of options (in units)			443,800	600,000
Proceeds from stock options exercised			$ 9,642	$ 10,802