Discontinued Operations and Held for Sale Businesses - Schedule of Balance Sheet and Income Statement Items (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
May 31, 2013	May 31, 2012	May 31, 2011
Assets:
Total Assets in Discontinued Operations Held for Sale	$ 0	$ 40,344
Revenue and Income:
Earnings on discontinued operations, net of taxes	35,044	5,548	4,559
Expanded shale and clay lightweight aggregates manufacturing business
Assets:
Inventory		30,072
Property Plant and Equipment		10,272
Total Assets in Discontinued Operations Held for Sale		40,344
Revenue and Income:
Revenue	47,484	52,898	49,908
Earnings on discontinued operations, before taxes (includes gain on sale of discontinued operations of $41.1 million)	52,574	8,187	6,541
Earnings on discontinued operations, net of taxes	$ 35,044	$ 5,548	$ 4,559

Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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