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				6 Months Ended
	Nov. 30, 2014		Nov. 30, 2013		Nov. 30, 2014		Nov. 30, 2013		May 31, 2014
Revenues:
Total revenues	$ 59,703	[1]	$ 57,876	[1]	$ 121,574	[1]	$ 118,044	[1]
Net Long-Lived Assets:
Total net long-lived assets	230,743	[2]			230,743	[2]			235,010	[2]
U.S.
Revenues:
Total revenues	50,245	[1]	48,911	[1]	101,397	[1]	99,137	[1]
Net Long-Lived Assets:
Total net long-lived assets	186,155	[2]			186,155	[2]			188,343	[2]
Other
Revenues:
Total revenues	9,458	[1],[3]	8,965	[1],[3]	20,177	[1],[3]	18,907	[1],[3]
Net Long-Lived Assets:
Total net long-lived assets	$ 44,588	[2],[3]			$ 44,588	[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.