Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	May 31, 2013	May 31, 2012	May 31, 2011	May 31, 2010
Supplemental Balance Sheet Information [Line Items]
Cash and cash equivalents	$ 61,296	$ 88,027	$ 116,432	$ 74,946
Receivables – net	126,922	98,836
Inventories	105,054	99,441
Deferred income taxes and prepaid expenses	27,294	19,007
Discontinued operations held for sale	0	40,344
TOTAL CURRENT ASSETS	320,566	345,655
Property, plant and equipment – net	1,226,396	1,185,325
Goodwill	40,575	1,715
Real estate and investments	29,471	20,865
Deferred income taxes and other charges	18,817	23,368
Investment in subsidiaries	0	0
Long-term intercompany receivables	0	0
TOTAL ASSETS	1,635,825	1,576,928	1,551,011
Accounts payable	69,061	64,825
Accrued interest, compensation and other	62,336	61,317
Current portion of long-term debt	1,872	1,214
TOTAL CURRENT LIABILITIES	133,269	127,356
LONG-TERM DEBT	657,935	656,949
Long-term intercompany payables	0	0
Deferred income taxes	12,067	0
OTHER CREDITS	79,090	96,352
Shareholders' equity	753,464	696,271	695,582
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,635,825	1,576,928
Parent Company
Supplemental Balance Sheet Information [Line Items]
Cash and cash equivalents	58,791	84,713	113,898	72,492
Receivables – net	0	0
Inventories	0	0
Deferred income taxes and prepaid expenses	615	99
Discontinued operations held for sale	0	0
TOTAL CURRENT ASSETS	59,406	84,812
Property, plant and equipment – net	0	0
Goodwill	0	0
Real estate and investments	1,080	664
Deferred income taxes and other charges	210,838	123,734
Investment in subsidiaries	1,028,330	987,519
Long-term intercompany receivables	167,778	246,298
TOTAL ASSETS	1,467,432	1,443,027
Accounts payable	46	108
Accrued interest, compensation and other	26,416	25,829
Current portion of long-term debt	0	4
TOTAL CURRENT LIABILITIES	26,462	25,941
LONG-TERM DEBT	650,245	650,245
Long-term intercompany payables	18,743	18,747
Deferred income taxes	0	0
OTHER CREDITS	52,042	51,823
Shareholders' equity	719,940	696,271
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,467,432	1,443,027
Guarantor Subsidiaries
Supplemental Balance Sheet Information [Line Items]
Cash and cash equivalents	2,505	3,314	2,534	2,454
Receivables – net	126,922	98,836
Inventories	105,054	99,441
Deferred income taxes and prepaid expenses	26,834	18,908
Discontinued operations held for sale	0	40,344
TOTAL CURRENT ASSETS	261,315	260,843
Property, plant and equipment – net	1,226,396	1,185,325
Goodwill	40,575	1,715
Real estate and investments	28,391	20,201
Deferred income taxes and other charges	7,744	7,356
Investment in subsidiaries	0	0
Long-term intercompany receivables	18,743	18,747
TOTAL ASSETS	1,583,164	1,494,187
Accounts payable	69,015	64,717
Accrued interest, compensation and other	36,075	35,488
Current portion of long-term debt	1,872	1,210
TOTAL CURRENT LIABILITIES	106,962	101,415
LONG-TERM DEBT	7,690	6,704
Long-term intercompany payables	167,778	246,298
Deferred income taxes	211,832	107,722
OTHER CREDITS	27,048	44,529
Shareholders' equity	1,061,854	987,519
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,583,164	1,494,187
Consolidating Adjustments
Supplemental Balance Sheet Information [Line Items]
Cash and cash equivalents	0	0	0	0
Receivables – net	0	0
Inventories	0	0
Deferred income taxes and prepaid expenses	(155)	0
Discontinued operations held for sale	0	0
TOTAL CURRENT ASSETS	(155)	0
Property, plant and equipment – net	0	0
Goodwill	0	0
Real estate and investments	0	0
Deferred income taxes and other charges	(199,765)	(107,722)
Investment in subsidiaries	(1,028,330)	(987,519)
Long-term intercompany receivables	(186,521)	(265,045)
TOTAL ASSETS	(1,414,771)	(1,360,286)
Accounts payable	0	0
Accrued interest, compensation and other	(155)	0
Current portion of long-term debt	0	0
TOTAL CURRENT LIABILITIES	(155)	0
LONG-TERM DEBT	0	0
Long-term intercompany payables	(186,521)	(265,045)
Deferred income taxes	(199,765)	(107,722)
OTHER CREDITS	0	0
Shareholders' equity	(1,028,330)	(987,519)
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ (1,414,771)	$ (1,360,286)

Represents deferred tax assets net, current and prepaid expense, current. Deferred Tax Assets, Net, Current represents the current portion of the aggregate tax effects as of the balance sheet date of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws; after deducting the allocated valuation allowance, if any, to reduce such amount to net realizable value. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. An unrecognized tax benefit that is directly related to a position taken in a tax year that results in a net operating loss carryforward should be presented as a reduction of the related deferred tax asset. Prepaid expense, current represents the sum of the amounts paid in advance for capitalized costs that will be expensed with the passage of time or the occurrence of a triggering event, and will be charged against earnings within one year or the normal operating cycle, if longer.

No definition available.