Intangible Assets and Goodwill - Components of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 28,703	$ 18,694
Less accumulated amortization	(17,029)	(15,724)
Intangible assets	11,674	2,970
Covenants Not to Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets	17,043	15,601
Less accumulated amortization	(14,800)	(14,324)
Intangible assets	2,243	1,277
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets	11,660	3,093
Less accumulated amortization	(2,229)	(1,400)
Intangible assets	$ 9,431	$ 1,693

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant