CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Aug. 31, 2015	May. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 553	$ 604
Accumulated depreciation on rental and lease equipment	237,652	241,116
Accumulated depreciation and amortization for other property	16,983	16,749
Accumulated amortization of intangibles	$ 1,790	$ 1,761
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	24,126,792	24,008,489
Common stock, shares outstanding	24,126,792	24,008,489