Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
AB Holding Units purchased (in units)	1,200,000	4,300,000	1,200,000	5,700,000
Amount paid for AB Holding Units acquired	$ 32,900	$ 96,700	$ 35,200	$ 127,800
Open-market purchases of AB Holding Units (in units)	1,200,000	3,700,000		4,900,000
Amount paid for open-market purchases of AB Holding Units	$ 32,900	$ 82,400		$ 110,300
Units granted to employees and Eligible Directors (in units)			2,400,000	2,000,000
Units issued upon exercise of options (in units)			488,513	500,000
Proceeds from stock options exercised			$ 8,340	$ 9,246