Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
AB Holding Units purchased (in units)	300,000	2,000,000	5,900,000	5,800,000
Amount paid for AB Holding Units acquired	$ 6,900	$ 45,200	$ 134,600	$ 129,200
Open-market purchases of AB Holding Units (in units)	300,000	2,000,000	5,200,000	5,700,000
Amount paid for open-market purchases of AB Holding Units	$ 6,800	$ 45,100	$ 117,100	$ 127,100
Restricted AB Holding Units awarded to employees (in units)			2,200,000	700,000
Units issued upon exercise of options (in units)			1,039,632	100,000
Proceeds from stock options exercised			$ 17,672	$ 2,371