Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Aug. 31, 2013	Aug. 31, 2012
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	$ (6,072)	$ 2,092
Capital expenditures – expansions	(7,125)	(28,114)
Capital expenditures – other	(5,373)	(4,496)
Proceeds from asset disposals	4,319	3,578
Investments in life insurance contracts	934	146
Other – net	0	(59)
Net cash provided (used) by investing activities	(7,245)	(28,945)
Debt payments	(447)	(1,028)
Stock option exercises	940	725
Net intercompany financing activities	0	0
Net cash used by financing activities	493	(303)
Decrease in cash and cash equivalents	(12,824)	(27,156)
Cash and cash equivalents at beginning of period	61,296	88,027
Cash and cash equivalents at end of period	48,472	60,871
Parent Company
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	(31,062)	(30,309)
Capital expenditures – expansions	0	0
Capital expenditures – other	0	0
Proceeds from asset disposals	0	0
Investments in life insurance contracts	934	146
Other – net		0
Net cash provided (used) by investing activities	934	146
Debt payments	0	(4)
Stock option exercises	940	725
Net intercompany financing activities	15,429	(2,277)
Net cash used by financing activities	16,369	(1,556)
Decrease in cash and cash equivalents	(13,759)	(31,719)
Cash and cash equivalents at beginning of period	58,791	84,713
Cash and cash equivalents at end of period	45,032	52,994
Guarantor Subsidiaries
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	24,990	32,401
Capital expenditures – expansions	(7,125)	(28,114)
Capital expenditures – other	(5,373)	(4,496)
Proceeds from asset disposals	4,319	3,578
Investments in life insurance contracts	0	0
Other – net		(59)
Net cash provided (used) by investing activities	(8,179)	(29,091)
Debt payments	(447)	(1,024)
Stock option exercises	0	0
Net intercompany financing activities	(15,429)	2,277
Net cash used by financing activities	(15,876)	1,253
Decrease in cash and cash equivalents	935	4,563
Cash and cash equivalents at beginning of period	2,505	3,314
Cash and cash equivalents at end of period	3,440	7,877
Consolidation, Eliminations
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	0	0
Capital expenditures – expansions	0	0
Capital expenditures – other	0	0
Proceeds from asset disposals	0	0
Investments in life insurance contracts	0	0
Other – net		0
Net cash provided (used) by investing activities	0	0
Debt payments	0	0
Stock option exercises	0	0
Net intercompany financing activities	0	0
Net cash used by financing activities	0	0
Decrease in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	$ 0	$ 0