Stock-based Compensation - Summary of stock option activity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
Jan. 31, 2013
Number of Options [Roll Forward]
Outstanding at July 31, 2012	16,179
Grants of options	271
Exercises	(1,338)
Forfeitures or expirations	(33)
Outstanding at January 31, 2013	15,079
Exercisable at January 31, 2013	10,419
Weighted- average Exercise Price [Roll Forward]
Outstanding at July 31, 2012	$ 16.24
Grants of options	$ 29.19
Exercises	$ 13.63
Forfeitures or expirations	$ 26.08
Outstanding at January 31, 2013	$ 16.68
Exercisable at January 31, 2013	$ 15.89
Weighted-Average Remaining Contractual Term [Roll Forward]
Outstanding	6 years 4 months 6 days
Exercisable	5 years 11 months 5 days
Aggregate Intrinsic Value [Roll Forward]
Outstanding at January 31, 2013	$ 289,944
Exercisable at January 31, 2013	$ 208,545

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The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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Number of share options (or share units) exercised during the current period.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options outstanding.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which grantees can acquire the shares reserved for issuance on stock options awarded.

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