Segment Reporting - Sales, Attributed to Area to Which Product was Shipped (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Aug. 31, 2013	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	$ 117,427	$ 121,719	$ 110,082	$ 118,022	$ 110,223	$ 111,283	$ 103,477	$ 108,168	$ 467,250	$ 433,151	$ 373,763
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									429,957	400,070	346,893
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									8,662	5,653	4,027
Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									11,419	12,761	9,221
Columbia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									7,379	6,678	6,802
Japan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									5,112	4,380	3,434
Other Country [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									4,721	3,609	3,386
Non-United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									$ 37,293	$ 33,081	$ 26,870