Acquisitions and Divestitures (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Provision (benefit) for income taxes	$ 0	$ (0.8)	$ 1.1
Net income (loss) from discontinued operations	0	(0.8)	1.8
Ready-mix concrete operations
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Revenues	0	31.6	121.4
Income (loss) from discontinued operations before income taxes	0	(1.6)	2.9
Provision (benefit) for income taxes	0	(0.8)	1.1
Net income (loss) from discontinued operations	$ 0	$ (0.8)	$ 1.8