Segment Reporting and Related Disclosures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2012	Nov. 30, 2011	Nov. 30, 2012	Nov. 30, 2011
Revenues from rental, lease and sale segment
Rentals and leases	$ 34,575	$ 32,912	$ 68,240	$ 64,221
Sales of equipment and other revenues	30,617	28,731	55,453	56,072
Total revenues	65,192	61,643	123,693	120,293
T&M [Member]
Revenues from rental, lease and sale segment
Rentals and leases	30,435	28,651	60,040	55,253
Sales of equipment and other revenues	29,944	28,113	54,091	54,829
Total revenues	60,379	56,764	114,131	110,082
DP [Member]
Revenues from rental, lease and sale segment
Rentals and leases	4,140	4,261	8,200	8,968
Sales of equipment and other revenues	673	618	1,362	1,243
Total revenues	$ 4,813	$ 4,879	$ 9,562	$ 10,211