Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	$ 33,205	$ 24,978
Capital expenditures – expansions	(7,125)	(36,118)
Capital expenditures – other	(17,295)	(10,845)
Proceeds from asset disposals	7,682	3,958
Investments in life insurance contracts	4,059	2,366
Other – net	0	(88)
Net cash provided (used) by investing activities	(12,679)	(40,727)
Debt payments	(910)	(1,585)
Stock option exercises	1,450	1,089
Net intercompany financing activities	0	0
Net cash used by financing activities	540	(496)
Increase (decrease) in cash and cash equivalents	21,066	(16,245)
Cash and cash equivalents at beginning of period	61,296	88,027
Cash and cash equivalents at end of period	82,362	71,782
Parent Company
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	64,720	(37,559)
Capital expenditures – expansions	0	0
Capital expenditures – other	0	0
Proceeds from asset disposals	0	0
Investments in life insurance contracts	4,059	2,366
Other – net		0
Net cash provided (used) by investing activities	4,059	2,366
Debt payments	0	(8)
Stock option exercises	1,450	1,089
Net intercompany financing activities	(50,950)	17,755
Net cash used by financing activities	(49,500)	18,836
Increase (decrease) in cash and cash equivalents	19,279	(16,357)
Cash and cash equivalents at beginning of period	58,791	84,713
Cash and cash equivalents at end of period	78,070	68,356
Guarantor Subsidiaries
Cash Flow Supplemental Disclosures [Line Items]
Net cash provided (used) by operating activities	(31,515)	62,537
Capital expenditures – expansions	(7,125)	(36,118)
Capital expenditures – other	(17,295)	(10,845)
Proceeds from asset disposals	7,682	3,958
Investments in life insurance contracts	0	0
Other – net		(88)
Net cash provided (used) by investing activities	(16,738)	(43,093)
Debt payments	(910)	(1,577)
Stock option exercises	0	0
Net intercompany financing activities	50,950	(17,755)
Net cash used by financing activities	50,040	(19,332)
Increase (decrease) in cash and cash equivalents	1,787	112
Cash and cash equivalents at beginning of period	2,505	3,314
Cash and cash equivalents at end of period	4,292	3,426
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
Increase (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