Rental Equipment (Annual) (Detail) - Rental Equipment (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Rental equipment	$ 43,491	$ 43,252	$ 50,229
Less accumulated depreciation	28,001	27,060	30,173
Net rental equipment	$ 15,490	$ 16,192	$ 20,056

This element represents capitalized assets classified as property, plant and equipment not otherwise defined in the taxonomy.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 5

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Name:	us-gaap_PropertyPlantAndEquipmentOther
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant