Acquisitions and Divestitures (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Disposal Group, Including Discontinued Operation, Unclassified Balance Sheet Disclosures [Abstract]
Total assets of Ready-Mix Concrete Operations	$ 27.9				$ 32.5				$ 27.9	$ 32.5
Total liabilities of Ready-Mix Concrete Operations	3.7				2.7				3.7	2.7
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Provision (benefit) for income taxes									1.1	(0.4)	3.6
Net income (loss) from discontinued operations	(0.2)	0.7	1.4	(0.1)	(0.4)	0.5	0	(1.2)	1.8	(1.1)	6.0
Ready Mix Concrete Operations
Disposal Group, Including Discontinued Operation, Unclassified Balance Sheet Disclosures [Abstract]
Inventories	4.5				5.3				4.5	5.3
Property, plant, and equipment, net	16.9				20.4				16.9	20.4
Goodwill	6.3				6.4				6.3	6.4
Other	0.2				0.4				0.2	0.4
Total assets of Ready-Mix Concrete Operations	27.9				32.5				27.9	32.5
Debt	3.7				2.7				3.7	2.7
Total liabilities of Ready-Mix Concrete Operations	3.7				2.7				3.7	2.7
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Revenues									121.4	136.8	224.8
Income (loss) from discontinued operations before income taxes									2.9	(1.5)	9.6
Provision (benefit) for income taxes									1.1	(0.4)	3.6
Net income (loss) from discontinued operations									$ 1.8	$ (1.1)	$ 6.0