Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Feb. 29, 2012	May 31, 2011
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 482	$ 602
Accumulated depreciation on rental and lease equipment	199,515	191,160
Accumulated depreciation and amortization for other property	17,587	16,825
Amortization of intangibles	$ 1,263	$ 1,151
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	23,987,826	23,980,581
Common stock, shares outstanding	23,987,826	23,980,581