Notes Payable - Additional Information (Detail) (USD $)	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Debt Disclosure [Line Items]
Debt issuance costs	$ 10,194,000	$ 12,516,000
Senior term note	430,534,000	434,854,000
2018 Senior Notes
Debt Disclosure [Line Items]
Convertible senior notes, fixed interest rate	3.50%
Description of long term debt	Convertible senior notes, due 2018, bear interest at a fixed rate of 3.5%, paid semi-annually in arrears on April 1stand October 1st.
Convertible notes maturity date	Apr. 01, 2018
Convertible notes initial conversion rate, shares	26.2838
Convertible notes initial conversion rate, principal amount	1,000
Convertible notes initial conversion rate, per share	$ 38.05
Debt issuance costs	7,900,000
2026 Senior Notes
Debt Disclosure [Line Items]
Convertible senior notes, fixed interest rate	2.375%
Description of long term debt	Convertible senior notes, due 2026, bear interest at a fixed rate of 2.375%, paid semi-annually in arrears on May 15thand November 15th.
Convertible notes initial conversion rate, shares	20.8125
Convertible notes initial conversion rate, principal amount	1,000
Convertible notes initial conversion rate, per share	$ 48.05
Contingent interest rate	0.375%
Commencement date of contingent interest rate	May 15, 2013
Contingency period for interest payment	6 months
Percentage of notes redemption price	100.00%
Repurchase of notes description	On May 15, 2013, May 15, 2016 and May 15, 2021 or in the event of certain fundamental changes, holders can require the Company to repurchase all or a portion of their notes at a price equal to 100% of the principal amount of the notes plus accrued and unpaid interest.
Repurchase percentage price of principal of notes amount	100.00%
Equity component of debt	14,900,000	14,900,000
Accretion of debt discount, before tax	3,200,000	3,000,000	3,800,000
2026 Senior Notes | For the year ending August 31, 2013
Debt Disclosure [Line Items]
Expected accretion expense	2,500,000
Senior Notes Due March Twenty Fourteen
Debt Disclosure [Line Items]
Senior term note	100,000,000
Floating interest on borrowings above LIBOR rate	1.00%
Periodic principal payment	700,000
Ballon payment	81,800,000
Debt instrument amount outstanding	85,800,000
Swap agreement interest rate	50.00%
Fixed interest rate	5.24%
Notional amount of note	42,900,000
Senior Notes Due May Twenty Fifteen
Debt Disclosure [Line Items]
Senior term note	50,000,000
Floating interest on borrowings above LIBOR rate	1.00%
Periodic principal payment	300,000
Ballon payment	41,200,000
Debt instrument amount outstanding	44,600,000
Term Loan Due October Twenty Thirteen
Debt Disclosure [Line Items]
Senior term note	1,800,000
Floating interest on borrowings above LIBOR rate	2.50%
Periodic principal payment	200,000
Debt instrument amount outstanding	600,000
Term Loan Due December Twenty Twelve
Debt Disclosure [Line Items]
Senior term note	1,200,000
Floating interest on borrowings above LIBOR rate	4.00%
Debt instrument amount outstanding	1,200,000
Term Loan Due November Twenty Fifteen
Debt Disclosure [Line Items]
Senior term note	300,000
Periodic principal payment	3,000
Ballon payment	200,000
Debt instrument amount outstanding	$ 300,000