Acquisitions and Divestitures (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012	Dec. 31, 2012
Disposal Group, Including Discontinued Operation, Unclassified Balance Sheet Disclosures [Abstract]
Total assets of Ready-Mix Concrete Operations	$ 0	[1]		$ 0	[1]		$ 27.9
Total liabilities of Ready-Mix Concrete Operations	0	[1]		0	[1]		3.7
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net income (loss) from discontinued operations	(1.1)		1.4	(1.5)		1.3
Ready-Mix Concrete Operations
Disposal Group, Including Discontinued Operation, Unclassified Balance Sheet Disclosures [Abstract]
Inventories	0			0			4.5
Property, plant, and equipment, net	0			0			16.9
Goodwill	0			0			6.3
Other	0			0			0.2
Total assets of Ready-Mix Concrete Operations	0			0			27.9
Debt	0			0			3.7
Total liabilities of Ready-Mix Concrete Operations	0			0			3.7
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Revenues	0		32.8	31.6		61.9
Income (loss) from discontinued operations before income taxes	(1.6)		2.3	(2.3)		2.1
Income tax expense (benefit)	(0.5)		0.9	(0.8)		0.8
Net income (loss) from discontinued operations	$ (1.1)		$ 1.4	$ (1.5)		$ 1.3

[1] (unaudited)