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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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No definition available.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

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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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The weighted average period between the balance sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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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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The combined weighted average exercise price associated with stock options during the period that have either lapsed or been forfeited.

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

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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 stock options awarded under the plan during the reporting period.

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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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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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The weighted average period between the balance sheet date and expiration for all awards outstanding under the plan, which may be expressed in a decimal value for number of years.

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Stock-based Compensation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012	Jan. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense	$ 5,495	$ 4,479	$ 11,028	$ 9,116
Number Of Options [Roll Forward]
Outstanding			8,353
Grants of options			375
Exercises			(245)
Forfeitures or expirations			(19)
Outstanding	8,464		8,464
Exercisable	4,693		4,693
Weighted Average Exercise Price [Roll Forward]
Outstanding			$ 31.00
Grants of options	$ 45.11		$ 45.11
Exercises			$ 25.70
Forfeitures or expirations			$ 33.33
Outstanding	$ 31.77		$ 31.77
Exercisable	$ 29.35		$ 29.35
Weighted-Average Remaining Contractual Term [Roll Forward]
Outstanding	6.88		6.88
Exercisable			6.03
Aggregate Intrinsic Value [Roll Forward]
Outstanding	129,261		129,261
Exercisable	83,043		83,043
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense	4,793	4,230	9,643	8,561
Yard operations
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense	$ 702	$ 249	$ 1,385	$ 555