Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Feb. 28, 2013	May 31, 2012
Accounts and notes receivable, reserves	$ 1,330	$ 1,066
Preferred Stock, par (in dollars per share)	$ 1	$ 1
Preferred Stock, authorized	1,000,000	1,000,000
Preferred Stock, issued	0	0
Cost of Common Stock in treasury, shares	3,914,549	2,298,904
Common Stock [Member]
Common Stock, par (in dollars per share)	$ 1	$ 1
Common Stock, authorized	50,000,000	50,000,000
Common Stock, issued	22,426,249	22,372,198
Class B Common Stock [Member]
Common Stock, par (in dollars per share)	$ 1	$ 1
Common Stock, authorized	33,000,000	33,000,000
Common Stock, issued	8,763,264	8,817,315
Common Stock, outstanding	8,763,264	8,817,315