Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Feb. 29, 2012	May 31, 2011
Condensed Consolidated Balance Sheets
Accounts receivable, allowances (in dollars)	$ 6,840	$ 5,719
Property, plant and equipment, accumulated depreciation (in dollars)	$ 284,385	$ 235,098
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, authorized shares	250	250
Preferred stock, issued shares	0	0
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, authorized shares	100,000	100,000
Common stock, issued shares	44,896	44,986
Treasury stock, shares	4,608	5,205