Segment Reporting and Related Disclosures - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
May 31, 2013 Customer Segment	May 31, 2012 Customer	May 31, 2011 Customer
Revenue from External Customer [Line Items]
Number of operating segment	2
Number of major customer accounted for more than 10% of total revenues	0	0	0
T&M equipment
Revenue from External Customer [Line Items]
Equipment pool, based on acquisition cost	$ 423,306	$ 409,686
DP equipment
Revenue from External Customer [Line Items]
Equipment pool, based on acquisition cost	$ 35,947	$ 37,595

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration