Income Taxes - Principal Reasons for the Difference Between the Effective Tax Rate and Statutory Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Credit for UBT	4.00%	4.00%	4.00%
AB Holding's effective tax expense [Abstract]
UBT statutory rate	$ 9,576	$ 8,403	$ 8,037
Federal tax on partnership gross business income	22,342	23,845	22,131
State income taxes	461	475	332
Credit for UBT paid by AB	(9,576)	(8,403)	(8,037)
Income taxes	$ 22,803	$ 24,320	$ 22,463
AB Holding' effective tax rate [Abstract]
UBT statutory rate, percent	4.00%	4.00%	4.00%
Federal tax on partnership gross business income, percent	9.30%	11.40%	11.00%
State income taxes, percent	0.20%	0.20%	0.20%
Credit for UBT paid by AB, percent	(4.00%)	(4.00%)	(4.00%)
Income tax effective tax rate, percent	9.50%	11.60%	11.20%