Schedule of Major Classifications of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014	Jul. 31, 2013
Inventory [Line Items]
Raw materials	$ 121,535	$ 99,154
Chassis	50,804	34,108
Work in process	53,486	36,188
Finished goods	35,885	9,888
Total	261,710	179,338
Excess of FIFO costs over LIFO costs	(27,322)	(26,302)
Total inventories	$ 234,388	$ 153,036