Significant Accounting Policies - Earnings Per Share (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Reconciliation [Abstract]
Income from continuing operations	$ 8.1	$ 10.8	$ 10.2	$ 1.1	$ 13.3	$ (3.1)	$ 2.5	$ (0.2)	$ 30.2	$ 12.5	$ 6.0
Income attributable to non-controlling interest									(3.1)	(0.5)	0
Income from continuing operations attributable to A&B									$ 27.1	$ 12.0	$ 6.0
Weighted Average Number Diluted Shares Outstanding Adjustment [Abstract]
Denominator for basic EPS - weighted average shares outstanding	48.8	48.8	48.7	48.7	48.6	43.1	43.1	43.0	48.7	44.4	42.6
Employee/director stock options and restricted stock units (in shares)									0.6	0.7	0.3
Weighted Average Number of Shares Outstanding, Diluted	49.3	49.3	49.3	49.2	49.2	43.8	43.7	43.6	49.3	45.1	42.9