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		2,807,000				2,807,000
Proceeds from exercise of options (in shares)	66,945					66,945
Proceeds from exercise of options	7,000	1,005,000				1,012,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	25,170					25,170
Proceeds from issuance of employee stock purchase plan shares	2,000	585,000				587,000
Cash dividends			(13,614,000)			(13,614,000)
(Income tax shortfall) excess income tax benefit from stock-based award exercises		113,000				113,000
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,237,000)				(1,237,000)
Repurchases of common stock (in shares)				1,628,848		1,628,848
Repurchases of common stock				(46,804,000)		(46,804,000)
Net income			41,752,000		41,752,000	41,752,000
Ending balance at Jan. 31, 2011	2,863,000	350,787,000	379,587,000	(46,989,000)	41,752,000	686,248,000
Common stock shares issued, end of period (in shares) at Jan. 31, 2011	28,634,650					28,634,650
Treasury stock shares outstanding, end of period (in shares) at Jan. 31, 2011				1,839,785		1,839,785
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		1,834,000				1,834,000
Proceeds from exercise of options (in shares)	114,160					114,160
Proceeds from exercise of options	12,000	2,575,000				2,587,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	23,664					23,664
Proceeds from issuance of employee stock purchase plan shares	2,000	554,000				556,000
Cash dividends			(11,454,000)			(11,454,000)
(Income tax shortfall) excess income tax benefit from stock-based award exercises		(81,000)				(81,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,186,000)				(1,186,000)
Repurchases of common stock (in shares)				5,066,292		5,066,292
Repurchases of common stock				(155,744,000)		(155,744,000)
Net income			18,422,000		18,422,000	18,422,000
Ending balance at Jan. 31, 2012	$ 2,887,000	$ 358,697,000	$ 400,077,000	$ (277,547,000)	$ 18,422,000	$ 484,114,000
Common stock shares issued, end of period (in shares) at Jan. 31, 2012	28,869,089					28,869,089
Treasury stock shares outstanding, end of period (in shares) at Jan. 31, 2012				9,574,737		9,574,737