Condensed Consolidated Statements of Stockholders' Equity and Comprehensive Income (USD $)	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Comprehensive Income [Member]	Total
Beginning balance at Jul. 31, 2010	$ 2,854,000	$ 347,514,000	$ 351,449,000	$ (185,000)		$ 701,632,000
Treasury stock shares outstanding, beginning of period (in shares) at Jul. 31, 2010				210,937		210,937
Common stock shares issued, beginning of period (in shares) at Jul. 31, 2010	28,542,535					28,542,535
Equity-classified stock award compensation		1,491,000				1,491,000
Proceeds from exercise of options (in shares)	37,795					37,795
Proceeds from exercise of options	4,000	609,000				613,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	12,319					12,319
Proceeds from issuance of employee stock purchase plan shares	1,000	285,000				286,000
Cash dividends			(6,915,000)			(6,915,000)
Income tax shortfall from stock-based award exercises		(3,000)				(3,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,033,000)				(1,033,000)
Repurchases of common stock (in shares)				720,996		720,996
Repurchases of common stock				(20,198,000)		(20,198,000)
Net income			25,656,000		25,656,000	25,656,000
Ending balance at Oct. 31, 2010	2,859,000	348,863,000	370,190,000	(20,383,000)	25,656,000	701,529,000
Common stock shares issued, end of period (in shares) at Oct. 31, 2010	28,592,649					28,592,649
Treasury stock shares outstanding, end of period (in shares) at Oct. 31, 2010				931,933		931,933
Beginning balance at Jul. 31, 2011	2,873,000	355,001,000	393,109,000	(121,803,000)		629,180,000
Treasury stock shares outstanding, beginning of period (in shares) at Jul. 31, 2011				4,508,445		4,508,445
Common stock shares issued, beginning of period (in shares) at Jul. 31, 2011	28,731,265					28,731,265
Equity-classified stock award compensation		853,000				853,000
Proceeds from exercise of options (in shares)	99,260					99,260
Proceeds from exercise of options	10,000	2,231,000				2,241,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	12,018					12,018
Proceeds from issuance of employee stock purchase plan shares	1,000	286,000				287,000
Cash dividends			(6,102,000)			(6,102,000)
Income tax shortfall from stock-based award exercises		(125,000)				(125,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,021,000)				(1,021,000)
Repurchases of common stock (in shares)				2,717,393		2,717,393
Repurchases of common stock				(81,152,000)		(81,152,000)
Net income			12,601,000		12,601,000	12,601,000
Ending balance at Oct. 31, 2011	$ 2,884,000	$ 357,225,000	$ 399,608,000	$ (202,955,000)	$ 12,601,000	$ 556,762,000
Common stock shares issued, end of period (in shares) at Oct. 31, 2011	28,842,543					28,842,543
Treasury stock shares outstanding, end of period (in shares) at Oct. 31, 2011				7,225,838		7,225,838