Shareholders' Equity (Details 1) (USD $)	3 Months Ended														12 Months Ended
	Jul. 31, 2011		Apr. 30, 2011		Jan. 31, 2011		Jul. 31, 2010		Oct. 31, 2009		Jul. 31, 2009		Jan. 31, 2009		Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009	Jan. 14, 2011
Stockholders' Equity, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, shares authorized	180,000,000						180,000,000								180,000,000	180,000,000
Common stock, no par value (in dollars per share)
Common stock, shares outstanding	66,005,517						84,363,063								66,005,517	84,363,063
Common stock, shares issued	66,005,517						84,363,063								66,005,517	84,363,063
Preferred stock, shares authorized	5,000,000														5,000,000
Preferred stock, no par value (in dollars per share)
Preferred stock, shares outstanding
Preferred stock, shares issued
Stock Repurchase [Abstract]
Common stock authorised for repurchase	29,000,000														29,000,000
Shares repurchased, shares															6,682,317	121,251
Stock repurchase price per share (in dollars per share)															$ 40.83	$ 36.76
Number of shares repurchased under the program	20,453,037														20,453,037
Number of shares repurchased under the program as of 31st July, 2010							8,546,963									8,546,963
Purchase of common shares from tender offer																		10,526,315
Tender price to purchase common shares																		$ 38
Number of shares accepted for purchase under tender offer																		12,172,088
Additional purchase of common shares from tender offer																		1,645,773
Dilutive earnings per share, Impact of Repurchase Shares (in dollars per share)															$ 0.23
Remittance by the company to the taxing authorities under statutory withholding requirements															$ 4,200,000	$ 7,400,000	$ 9,800,000
Share-Based Compensation Arrangement By Share-Based Payment Award, Options Exercisable [Abstract]
Options Exercised	90,000		274,167		88,750		350,000		323,631		361,035		600,000		(726,000)
Exercises	$ 18.95		$ 22.03		$ 16.93		$ 12.91		$ 13.03		$ 11.12		$ 4.47		$ 18.95	$ 12.91	$ 11.12
Shares Net Settled for Exercise	38,198		147,748		38,025		122,922		114,354		116,741		96,929
Shares Withheld for Taxes (1)	24,183	[1]	59,016	[1]	18,917	[1]	105,827	[1]	95,746	[1]	109,595	[1]	222,817	[1]
Net Shares to Employee	27,619		67,403		31,808		121,251		113,531		134,699		280,254
Share Price for Withholding	$ 44.65		$ 40.80		$ 39.51		$ 36.76		$ 36.89		$ 34.39		$ 26.93		$ 44.65	$ 36.76	$ 34.39
Tax Withholding (in 000's)	$ 1,080,000		$ 2,408,000		$ 748,000		$ 3,890,000		$ 3,532,000		$ 3,769,000		$ 6,000,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, reserved for issuance of Stock Options	711,710						775,306								711,710	775,306
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, reserved for issuance of Stock Options	9,825,924						10,630,904								9,825,924	10,630,904

[1] Shares withheld for taxes are treated as a repurchase of shares for accounting purposes but do not count against the Company's stock repurchase program.