Income Taxes (Details 2) (USD $)	3 Months Ended								12 Months Ended
	Aug. 31, 2011	May 31, 2011	Feb. 28, 2011	Nov. 30, 2010	Aug. 31, 2010	May 31, 2010	Feb. 28, 2010	Nov. 30, 2009	Aug. 31, 2011	Aug. 31, 2010	Aug. 31, 2009
Income tax examination [Line Items]
Cash paid									$ 464,701,000	$ 514,532,000	$ 472,241,000
Income tax benefit	44,622,000	130,385,000	76,052,000	169,579,000	122,628,000	122,390,000	69,064,000	149,981,000	420,638,000	464,063,000	456,720,000
Increase in additional paid-in capital										27,484,000
IRS (Lawsuit Settlement Deductibility) [Member]
Income tax examination [Line Items]
Income tax benefit									(9,600,000)
IRS (Years 2003 Through 2005) [Member]
Income tax examination [Line Items]
Reserve for uncertain tax positions prior to settlement								50,500,000
Cash paid										27,300,000
Income tax benefit										(10,200,000)
Decrease in deferred tax assets					1,500,000					1,500,000
Increase in additional paid-in capital										11,500,000
IRS (Years 2006 Through 2009) [Member]
Income tax examination [Line Items]
Income tax benefit										(1,200,000)
Decrease in deferred tax assets					900,000					900,000
Increase in additional paid-in capital										16,000,000
Arizona Department of Revenue [Member]
Income tax examination [Line Items]
Income tax benefit									(43,300,000)
Income tax refund claim										51,500,000
Tax settlement that we paid or will pay	$ 59,800,000								$ 59,800,000