Discontinued Operations - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Oct. 20, 2013	Jan. 31, 2014	Apr. 30, 2013	Jan. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of bus business		$ 2,323		$ 100,000
Discontinued operation, amounts due from ASV	5,043
Pre-tax gain on sale of business		(746)		7,079
Disposition of ambulance net assets			12,051
Gain (loss) recognized on sale of assets			0
Impact of indemnification to tax expenses		$ 1,883		$ 1,883