Shareholders' Equity (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	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
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense								$ 19,007	$ 17,955	$ 9,413
Number Of Shares [Roll Forward]
Non-vested shares at July 31								4,633,000
Grants of options								1,117,000
Vested								(1,496,000)
Forfeitures or expirations								(90,000)
Non-vested shares at July 31	4,164,000			4,633,000				4,164,000	4,633,000
Weighted Average Grant Date Fair Value [Roll Forward]
Non-vested shares at July 31 (in dollars per share)								$ 13.23
Grants of options (in dollars per share)								$ 13.40
Vested (in dollars per share)								$ 13.10
Forfeitures or expirations (in dollars per share)	$ 12.50							$ 12.50
Non-vested shares at July 31 (in dollars per share)	$ 13.32			$ 13.23				$ 13.32	$ 13.23
Number Of Options [Roll Forward]
Outstanding at July 31, 2010								8,052,000
Grants of options								1,117,000
Options Exercised	90,000	274,167	88,750	350,000	323,631	361,035	600,000	(726,000)
Forfeitures or expirations								(90,000)
Outstanding at July 31	8,353,000			8,052,000				8,353,000	8,052,000
Exercisable at July 31, 2011	4,189,000							4,189,000
Vested and expected to vest at July 31, 2011	8,031,000							8,031,000
Weighted Average Exercise Price [Roll Forward]
Outstanding at July 31 (in dollars per share)								$ 29.07
Grants of options (in dollars per share)	$ 38.46							$ 38.46
Exercises (in dollars per share)	$ 21.11							$ 21.11
Forfeitures or expirations (in dollars per share)								$ 33.71
Outstanding at July 31 (in dollars per share)	$ 31			$ 29.07				$ 31	$ 29.07
Exercisable at July 31, 2011 (in dollars per share)	$ 28.67							$ 28.67
Vested and expected to vest at July 31, 2011 (in dollars per share)	$ 31.01							$ 31.01
Weighted-Average Remaining Contractual Term [Roll Forward]
Outstanding at July 31								7.49
Outstanding at July 31	7.18			7.49				7.18	7.49
Exercisable at July 31, 2011								6.21
Vested and expected to vest at July 31, 2011								7.19
Aggregate Intrinsic Value [Roll Forward]
Outstanding at July 31 (in dollars)								60,151
Outstanding at July 31 (in dollars)	103,979			60,151				103,979	60,151
Vested and expected to vest at July 31, 2011 (in dollars)	99,933							99,933
Exercisable at July 31, 2011 (in dollars)	61,935							61,935
Yard Operations
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense								1,031	1,109	1,220
General and Administrative Expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense								$ 17,976	$ 16,846	$ 8,193