Long-Term Debt (Details)	12 Months Ended				12 Months Ended				12 Months Ended			1 Months Ended	12 Months Ended
	Aug. 31, 2014 USD ($)	Aug. 31, 2013 USD ($)	Aug. 31, 2014 For Certain Obligations, Workers Compensation and Performance Bonds USD ($)	Aug. 31, 2013 For Certain Obligations, Workers Compensation and Performance Bonds USD ($)	Aug. 31, 2014 Capital Lease Obligations	Aug. 31, 2014 Bank of America NA And Other Lenders USD ($)	Aug. 31, 2014 Bank of America NA And Other Lenders CAD	Aug. 31, 2013 Bank of America NA And Other Lenders USD ($)	Aug. 31, 2014 Bank of America NA And Other Lenders Minimum	Aug. 31, 2014 Bank of America NA And Other Lenders Maximum	Aug. 31, 2014 Bank of America NA And Other Lenders Interest Rate Option 1	Apr. 30, 2012 Bank of America NA And Other Lenders Interest Rate Option 1 Minimum	Aug. 31, 2014 Bank of America NA And Other Lenders Interest Rate Option 1 Maximum	Aug. 31, 2014 Bank of America NA And Other Lenders Interest Rate Option 2	Aug. 31, 2014 Bank of America NA And Other Lenders Interest Rate Option 3
Debt Instrument [Line Items]
Bank unsecured revolving credit facility, interest at LIBOR plus a spread						$ 305,000,000		$ 359,971,000
Tax-exempt economic development revenue bonds due January 2021, interest payable monthly at a variable rate (0.10% as of August 31, 2014), secured by a letter of credit	7,700,000	7,700,000
Tax-exempt economic development revenue bonds, variable interest rate	0.10%
Tax Exempt Economic Development Revenue Bond Due Date	Jan. 31, 2021
Capital lease obligations due through April 2031	5,655,000	5,666,000
Other Long-term Debt	1,010,000	0
Capital lease obligations due date					Apr. 30, 2031
Total Long-term debt	319,365,000	373,337,000
Less current maturities	(523,000)	(674,000)
Long-term debt, net of current maturities	318,842,000	372,663,000
Line of Credit Facility, Maximum Borrowing Capacity						670,000,000	30,000,000
Debt Instrument, Description of Variable Rate Basis											London Interbank Offered Rate (or the Canadian equivalent)			greater of the prime rate, the federal funds rate	British Bankers Association LIBOR Rate
Debt Instrument, Basis Spread on Variable Rate												1.25%	2.25%	0.50%	1.75%
Line of Credit Facility, Commitment Fee Percentage									0.15%	0.35%
Line of Credit Facility, Expiration Date						Apr. 30, 2017	Apr. 30, 2017
Line of Credit Facility, Amount Outstanding						305,000,000		359,971,000
Long-term Debt, Weighted Average Interest Rate						1.91%	1.91%	1.98%
Letters of Credit Outstanding, Amount			$ 16,000,000	$ 18,000,000