Segment Reporting and Related Disclosures - Revenues from External Customers and Long-Lived Assets, by Geographical Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Feb. 28, 2015		Feb. 28, 2014		Feb. 28, 2015		Feb. 28, 2014		May 31, 2014
Revenues:
Total revenues	$ 56,342	[1]	$ 62,016	[1]	$ 177,916	[1]	$ 180,060	[1]
Net Long-Lived Assets:
Total net long-lived assets	230,158	[2]			230,158	[2]			235,010	[2]
U.S.
Revenues:
Total revenues	47,922	[1]	52,638	[1]	149,320	[1]	151,775	[1]
Net Long-Lived Assets:
Total net long-lived assets	185,283	[2]			185,283	[2]			188,343	[2]
Other
Revenues:
Total revenues	8,420	[1],[3]	9,378	[1],[3]	28,596	[1],[3]	28,285	[1],[3]
Net Long-Lived Assets:
Total net long-lived assets	$ 44,875	[2],[3]			$ 44,875	[2],[3]			$ 46,667	[2],[3]

[1] Revenues by country are based on the shipping destination.

[2] Net long-lived assets include rental and lease equipment and other property, net of accumulated depreciation and amortization.

[3] Other consists of countries other than the U.S. Each foreign country individually accounts for less than 10% of the total revenues and long-lived assets.