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, 2008	$ 2,460,000	$ 205,204,000	$ 243,294,000	$ (185,000)		$ 450,773,000
Treasury stock shares outstanding, beginning of period (in shares) at Jul. 31, 2008				210,937		210,937
Common stock shares issued, beginning of period (in shares) at Jul. 31, 2008	24,600,166					24,600,166
Equity-classified stock award compensation		9,712,000				9,712,000
Proceeds from exercise of options (in shares)	410,403					410,403
Proceeds from exercise of options	41,000	8,243,000				8,284,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	46,959					46,959
Proceeds from issuance of employee stock purchase plan shares	5,000	1,301,000				1,306,000
(Income tax shortfall) excess income tax benefit from stock based award exercises		2,530,000				2,530,000
Debt converted to shares of common stock, shares (in shares)	3,333,327					3,333,327
Debt converted to shares of common stock	333,000	108,666,000				108,999,000
Net income			47,525,000		47,525,000	47,525,000
Ending balance at Jul. 31, 2009	2,839,000	335,656,000	290,819,000	(185,000)	47,525,000	629,129,000
Common stock shares issued, end of period (in shares) at Jul. 31, 2009	28,390,855					28,390,855
Treasury stock shares outstanding, end of period (in shares) at Jul. 31, 2009				210,937		210,937
Equity-classified stock award compensation		8,639,000				8,639,000
Proceeds from exercise of options (in shares)	103,478					103,478
Proceeds from exercise of options	10,000	1,661,000				1,671,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	48,202					48,202
Proceeds from issuance of employee stock purchase plan shares	5,000	1,301,000				1,306,000
(Income tax shortfall) excess income tax benefit from stock based award exercises		257,000				257,000
Net income			60,630,000		60,630,000	60,630,000
Ending balance at Jul. 31, 2010	2,854,000	347,514,000	351,449,000	(185,000)	60,630,000	701,632,000
Common stock shares issued, end of period (in shares) at Jul. 31, 2010	28,542,535					28,542,535
Treasury stock shares outstanding, end of period (in shares) at Jul. 31, 2010				210,937		210,937
Equity-classified stock award compensation		5,366,000				5,366,000
Proceeds from exercise of options (in shares)	139,885					139,885
Proceeds from exercise of options	14,000	2,824,000				2,838,000
Proceeds from issuance of employee stock purchase plan shares (in shares)	48,845					48,845
Proceeds from issuance of employee stock purchase plan shares	5,000	1,135,000				1,140,000
Cash dividends			(26,235,000)			(26,235,000)
(Income tax shortfall) excess income tax benefit from stock based award exercises		(53,000)				(53,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards		(1,785,000)				(1,785,000)
Repurchases of common stock (in shares)				4,297,508		4,297,508
Repurchases of common stock				(121,618,000)		(121,618,000)
Net income			67,895,000		67,895,000	67,895,000
Ending balance at Jul. 31, 2011	$ 2,873,000	$ 355,001,000	$ 393,109,000	$ (121,803,000)	$ 67,895,000	$ 629,180,000
Common stock shares issued, end of period (in shares) at Jul. 31, 2011	28,731,265					28,731,265
Treasury stock shares outstanding, end of period (in shares) at Jul. 31, 2011				4,508,445		4,508,445