Acquisitions and Divestitures (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Assets of Ready-Mix Concrete Operations:
Total assets of Ready-Mix Concrete Operations	$ 0	[1]		$ 0	[1]		$ 27.9
Liabilities of Ready-Mix Concrete Operations:
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	0.3		0.7	(1.2)		2.0
Ready-Mix Concrete Operations
Assets of Ready-Mix Concrete Operations:
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
Liabilities of Ready-Mix Concrete Operations:
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		30.2	31.6		92.2
Income (loss) from discontinued operations before income taxes	0.4		1.1	(1.9)		3.3
Income tax expense (benefit)	0.1		0.4	(0.7)		1.2
Net income (loss) from discontinued operations	$ 0.3		$ 0.7	$ (1.2)		$ 2.1

[1] (unaudited)