Common Stock Repurchases - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended		3 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jan. 31, 2012 Stock Repurchase Plan	Jul. 31, 2012 Stock Repurchase Plan	Dec. 09, 2010 Stock Repurchase Plan Maximum	Jul. 31, 2012 Stock Repurchase Plan Two	Dec. 08, 2011 Stock Repurchase Plan Two Maximum
Stockholders Equity Note [Line Items]
Amount authorized for repurchase of Company's common stock					$ 30,000		$ 30,000
Repurchase of common stock (in shares)			586,679	286,390		137,591
Repurchase of common stock	$ 23,260	$ 15,187	$ 30,000	$ 14,813		$ 8,447
Average purchase price of common stock			$ 51.14	$ 51.73		$ 61.39