Debt - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Nov. 30, 2009	Feb. 28, 2013 SecurityLoan
Line of credit, amount outstanding		$ 84,000,000
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)		0.02%
Covenant, fixed coverage ratio		1.35
2012 Agreement [Member] | Maximum [Member]
Debt Instrument, Description of Variable Rate Basis over LIBOR (in percentage)		0.04%
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 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		$ 1,300,000