Business Acquisitions - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2013 Property	Jul. 31, 2012 Property
Business Acquisition [Line Items]
Number of business acquired	0	1
Total consideration		$ 3,500
Business acquisition, cash		3,150
Business Acquisition [Member]
Business Acquisition [Line Items]
Business acquisition, hold backs to sellers		$ 350
Minimum [Member]
Business Acquisition [Line Items]
Acquired intangible assets, amortization period	5 years	5 years
Maximum [Member]
Business Acquisition [Line Items]
Acquired intangible assets, amortization period	10 years	10 years