Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Nov. 30, 2012	May 31, 2012
Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 466	$ 522
Accumulated depreciation on rental and lease equipment	215,366	204,108
Accumulated depreciation and amortization for other property	18,398	17,832
Amortization of intangibles	$ 1,386	$ 1,304
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued
Common stock, par value
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares issued	23,995,626	23,987,826
Common stock, shares outstanding	23,995,626	23,987,826