Schedule of Major Classifications of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2013	Jul. 31, 2012
Schedule of Inventory [Line Items]
Finished products	$ 9,888	$ 16,570
Work in process	36,188	59,803
Raw materials	99,154	104,446
Chassis	34,108	39,044
Subtotal	179,338	219,863
Excess of FIFO costs over LIFO costs	(26,302)	(33,780)
Total inventories	$ 153,036	$ 186,083