Condensed Consolidated Statements of Stockholders' Equity (USD $)	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [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		3,926,000			3,926,000
Proceeds from exercise of options (in shares)	82,795				82,795
Proceeds from exercise of options	8,000	1,297,000			1,305,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	36,814				36,814
Proceeds from issuance of employee stock purchase plan shares	4,000	853,000			857,000
Cash dividends			(20,135,000)		(20,135,000)
Net excess income tax benefit (shortfall) from stock-based award exercises		154,000			154,000
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,760,000)			(1,760,000)
Repurchases of common stock (in shares)				2,365,870	2,365,870
Repurchases of common stock				(68,071,000)	(68,071,000)
Net income			56,007,000		56,007,000
Ending balance at Apr. 30, 2011	2,866,000	351,984,000	387,321,000	(68,256,000)	673,915,000
Common stock shares issued, end of period (in shares) at Apr. 30, 2011	28,662,144				28,662,144
Treasury stock shares outstanding, end of period (in shares) at Apr. 30, 2011				2,576,807	2,576,807
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		2,652,000			2,652,000
Proceeds from exercise of options (in shares)	139,595				139,595
Proceeds from exercise of options	14,000	3,113,000			3,127,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	34,421				34,421
Proceeds from issuance of employee stock purchase plan shares	4,000	821,000			825,000
Cash dividends			(16,525,000)		(16,525,000)
Net excess income tax benefit (shortfall) from stock-based award exercises		(50,000)			(50,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,329,000)			(1,329,000)
Repurchases of common stock (in shares)				6,054,022	6,054,022
Repurchases of common stock				(188,061,000)	(188,061,000)
Net income			24,488,000		24,488,000
Ending balance at Apr. 30, 2012	$ 2,891,000	$ 360,208,000	$ 401,072,000	$ (309,864,000)	$ 454,307,000
Common stock shares issued, end of period (in shares) at Apr. 30, 2012	28,905,281				28,905,281
Treasury stock shares outstanding, end of period (in shares) at Apr. 30, 2012				10,562,467	10,562,467