Other Non-operating Income (Expense) - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Aug. 31, 2012	May 31, 2012	Aug. 31, 2012
Other Non Operating Income And Expenses [Line Items]
Derivative Instruments, Loss Recognized in Income			$ 1.0
Derivative Instruments, Loss Recognized in Income			1.6
Series A Preferred Stock [Member]
Other Non Operating Income And Expenses [Line Items]
Redeemed shares	58,750	41,250	41,250
Original issue price of redeemed shares	23.5	16.5	23.5
Accrued dividend of redeemed shares	5.4	3.5	3.5
Accelerated discount accretion	3.2		5.5
Amortization of issuance cost	0.6	0.5	1.1
Derivative Instruments, Loss Recognized in Income	$ 3.2	$ 2.3