Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
OPERATING ACTIVITIES
Net income (loss)	$ 7,476	$ (64,913)	$ (38,853)
Adjustments to reconcile net income (loss) to cash provided by operating activities
Depreciation, depletion and amortization	60,952	64,297	63,925
Gains on asset disposals	(67,610)	(13,638)	(1,350)
Deferred income tax benefit	(88)	(42,875)	(9,132)
Stock-based compensation expense	2,387	5,581	5,097
Excess tax benefits from stock-based compensation			(250)
Loss on debt retirements		29,619
Other-net	1,223	3,158	13,998
Changes in operating assets and liabilities
Receivables-net	(13,303)	13,379	(5,421)
Inventories	10,829	2,164	13,706
Prepaid expenses	1,385	1,301	387
Accounts payable and accrued liabilities	6,923	11,172	6,046
Net cash provided by operating activities	10,174	9,245	48,153
INVESTING ACTIVITIES
Capital expenditures-expansions	(72,906)	(25,430)	(5,337)
Capital expenditures-other	(33,430)	(20,253)	(8,322)
Proceeds from asset disposals	66,845	3,596	21,592
Investments in life insurance contracts	3,354	4,073	6,967
Other-net	(245)	1,266	2,079
Net cash provided (used) by investing activities	(36,382)	(36,748)	16,979
FINANCING ACTIVITIES
Long-term borrowings		650,000
Debt retirements	(300)	(561,627)	(245)
Debt issuance costs	(1,829)	(12,492)	(2,552)
Stock option exercises	2,023	1,462	893
Excess tax benefits from stock-based compensation			250
Common dividends paid	(2,091)	(8,354)	(8,328)
Net cash provided (used) by financing activities	(2,197)	68,989	(9,982)
Increase (decrease) in cash and cash equivalents	(28,405)	41,486	55,150
Cash and cash equivalents at beginning of year	116,432	74,946	19,796
Cash and cash equivalents at end of year	$ 88,027	$ 116,432	$ 74,946