Debt (Details) - USD ($)	3 Months Ended	6 Months Ended
	Feb. 29, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015
Debt [Line Items]
Total debt	$ 62,036,000	$ 62,036,000		$ 45,646,000
Less short-term borrowings and current portion of long-term debt	(20,961,000)	(20,961,000)		(14,080,000)
Long-term debt	41,075,000	41,075,000		31,566,000
Letters of credit outstanding	57,000,000	57,000,000		41,000,000
Revolving credit facility [Member]
Debt [Line Items]
Total debt	0	0		0
Borrowing capacity	625,000,000	$ 625,000,000
Debt term		5 years
Revolving credit facility borrowing	50,000,000
Debt repaid	50,000,000
Revolving credit facility [Member] | Minimum [Member]
Debt [Line Items]
Fees		0.25%
Revolving credit facility [Member] | Minimum [Member] | Prime Rate [Member]
Debt [Line Items]
Fees for borrowings		0.25%
Revolving credit facility [Member] | Maximum [Member]
Debt [Line Items]
Fees		0.40%
Revolving credit facility [Member] | Maximum [Member] | Prime Rate [Member]
Debt [Line Items]
Fees for borrowings		0.85%
Capital Lease Obligations [Member]
Debt [Line Items]
Total debt	33,076,000	$ 33,076,000		16,863,000
Notes Payable, Other Payables [Member]
Debt [Line Items]
Total debt	$ 28,960,000	$ 28,960,000		$ 28,783,000
Weighted average interest rate	5.90%	5.90%	5.60%