Debt - Additional Information (Detail) (USD $)	3 Months Ended
	Nov. 30, 2012 SecurityLoan	Nov. 30, 2009
Line of credit, amount outstanding	$ 81,600,000
2012 Agreement [Member]
Line of credit, amount outstanding	130,000,000
Dividend declared, Percentage of cash flow	50.00%
2012 Agreement [Member] | Two Consecutive Quarters [Member]
Covenant, total leverage ratio	2.50
2012 Agreement [Member] | Minimum [Member]
Debt Instrument, Description of Variable Rate Basis over LIBOR (in percentage)	2.00%
Covenant, fixed coverage ratio	1.35
2012 Agreement [Member] | Maximum [Member]
Debt Instrument, Description of Variable Rate Basis over LIBOR (in percentage)	4.00%
Covenant, total funded debt ratio after year three	3.0
Covenant, amount of annual capital expenditures permitted	15,000,000
Covenant, dividend declaration permitted	10,000,000
2012 Agreement [Member] | Maximum [Member] | Scenario, Forecast [Member]
Covenant, total leverage ratio	3.75
Covenant, total funded debt ratio year two	3.50
Covenant, total funded debt ratio year three	3.25
Iowa Department of Economic Development Loans [Member]
Number of monthly payments		60 equal monthly payments
Non interest bearing loans		1,000,000
Number of non interest bearing loans	2
Loan period (in years)	5 years
Potentially forgivable loan amount	1,000,000
Periodic repayments of loan		16,667
Outstanding amount of IDED loans	$ 1,400,000