Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
AB Holding Units purchased (in units)	100,000	1,300,000
Amount paid for AB Holding Units acquired	$ 2,300	$ 31,000
Open-market purchases of AB Holding Units (in units)		1,200,000
Amount paid for open-market purchases of AB Holding Units		$ 27,800
Restricted AB Holding Units awarded to employees (in units)	1,100,000	1,100,000
Units issued upon exercise of options (in units)	235,105	300,000
Proceeds from stock options exercised	$ 4,009	$ 4,468