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Discontinued Operations and Held for Sale Businesses - Additional Information (Details) (Expanded shale and clay lightweight aggregates manufacturing business, USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	Mar. 22, 2013 Property
Expanded shale and clay lightweight aggregates manufacturing business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of ready-mix concrete plants acquired		42
Number of distribution facilities acquired		2
Gain on sale of business	$ 41.1

Amount of gain (loss), before tax expense or benefit and not previously recognized, resulting from the sale of a business component.