Consolidated Statements of Shareholders' Equity (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified				9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended
	May 31, 2013 Common Stock ($1 par value)	May 31, 2012 Common Stock ($1 par value)	May 31, 2011 Common Stock ($1 par value)	Feb. 28, 2013 Retained Earnings	May 31, 2012 Retained Earnings	May 31, 2011 Retained Earnings	Feb. 28, 2013 Accumulated Other Comprehensive Loss	May 31, 2012 Accumulated Other Comprehensive Loss	May 31, 2011 Accumulated Other Comprehensive Loss
Common stock, par value (in USD per share)	$ 0	$ 1	$ 1
Common stock, dividends paid (in USD per share)				$ 0	$ 0.075	$ 0.30
Postretirement benefit obligation adjustments - tax expense (benefit)							$ 3,538	$ (1,367)	$ 800