Segment Results - Schedule of Segment Results (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Revenue		$ 144.7	$ 153.4	$ 449.1	$ 395.0
Operating profit		22.2	22.1	107.0	64.7
Interest expense		(6.5)	(7.2)	(20.2)	(21.6)
General corporate expenses		(4.8)	(3.9)	(15.7)	(13.5)
Reduction in KRS II carrying value		(0.1)	(15.1)	(1.7)	(15.1)
Income (Loss) From Continuing Operations Before Income Taxes		10.8	(4.1)	69.4	14.5
Income tax expense (benefit)		3.8	(14.9)	26.4	(7.6)
Income From Continuing Operations		7.0	10.8	43.0	22.1
Income From Discontinued Operations, net of income taxes		0.0	0.0	0.0	34.3
Net Income		7.0	10.8	43.0	56.4
Income attributable to noncontrolling interest		(0.3)	(0.6)	(1.2)	(2.0)
Net income attributable to A&B		6.7	10.2	41.8	54.4
Discontinued Operations
Segment Reporting Information [Line Items]
Revenue	[1]	0.0	0.0	0.0	(70.4)
Operating profit	[1]	0.0	0.0	0.0	(56.2)
Operating Segments | Leasing
Segment Reporting Information [Line Items]
Revenue	[1]	33.0	31.3	100.5	93.5
Operating profit	[1]	12.5	12.1	39.6	35.9
Operating Segments | Development and sales
Segment Reporting Information [Line Items]
Revenue	[1]	19.9	18.2	108.8	110.6
Operating profit	[1]	11.2	11.4	57.5	71.5
Operating Segments | Materials and construction
Segment Reporting Information [Line Items]
Revenue		51.0	58.4	165.3	173.1
Operating profit		7.5	5.9	21.7	17.3
Operating Segments | Agribusiness
Segment Reporting Information [Line Items]
Revenue		40.8	45.5	95.5	88.2
Operating profit		(9.0)	(7.3)	(11.8)	(3.8)
Reconciling item
Segment Reporting Information [Line Items]
Revenue	[2]	$ 0.0	$ 0.0	$ (21.0)	$ 0.0

[1] Prior year amounts recast for amounts treated as discontinued operations.

[2] Represents the sales of a Colorado retail property in March 2015 and a Texas office building in May 2015 that are classified as "Gain on the sale of improved property" in the Condensed Consolidated Statements of Income, but reflected as revenue for segment reporting purposes.