Supplemental Cash Flow Information (Details) (USD $)	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Supplemental Cash Flow Information [Abstract]
Income taxes paid, net of refunds	$ 74,199,000	$ 44,254,000	$ 72,649,000
Interest paid	13,631,000	15,537,000	12,728,000
Accrued liability for repurchase of common stock	0	0	1,920,000
Financing receivables:
Investment (sale) in equipment for financing leases	0	(54,000)	(1,932,000)
Principal collections from customers - financing leases	2,565,000	2,116,000	1,753,000
Net decrease in financing receivables	$ 2,565,000	$ 2,062,000	$ (179,000)