Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Nov. 30, 2011	Nov. 30, 2010
OPERATING ACTIVITIES
Net loss	$ (28,457)	$ (34,893)
Adjustments to reconcile net loss to cash provided by operating activities
Depreciation, depletion and amortization	31,385	31,991
Gains on asset disposals	(2,751)	(1,555)
Deferred income tax benefit	(945)	(22,964)
Stock-based compensation expense (credit)	(1,229)	2,288
Loss on debt retirements		29,619
Other - net	(5,185)	(2,855)
Changes in operating assets and liabilities
Receivables - net	3,696	16,112
Inventories	12,189	(10,262)
Prepaid expenses	2,854	1,232
Accounts payable and accrued liabilities	930	1,313
Net cash provided by operating activities	12,487	10,026
INVESTING ACTIVITIES
Capital expenditures - expansions	(35,966)	(11,198)
Capital expenditures - other	(26,300)	(12,201)
Proceeds from asset disposals	1,649	3,037
Investments in life insurance contracts	2,989	3,704
Other - net	(128)	(859)
Net cash used by investing activities	(57,756)	(17,517)
FINANCING ACTIVITIES
Long-term borrowings		650,000
Debt retirements	(36)	(561,568)
Debt issuance costs	(1,732)	(12,426)
Stock option exercises	158	464
Common dividends paid	(2,091)	(4,172)
Net cash provided (used) by financing activities	(3,701)	72,298
Increase (decrease) in cash and cash equivalents	(48,970)	64,807
Cash and cash equivalents at beginning of period	116,432	74,946
Cash and cash equivalents at end of period	$ 67,462	$ 139,753