Debt - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Nov. 30, 2009	May 31, 2013 SecurityLoan
Line of credit, amount outstanding		$ 77,000,000
2012 Agreement [Member]
Line of credit, amount outstanding		130,000,000
Debt instrument maturity date		Jul. 09, 2017
Dividend declared, Percentage of cash flow		50.00%
2012 Agreement [Member] | Two Consecutive Quarters [Member]
Covenant, maximum total leverage ratio permitted through November 30, 2013		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, maximum total leverage ratio permitted through November 30, 2013		3.50
Covenant, maximum total leverage ratio permitted from December 1, 2013 through May 31, 2014		3.25
Covenant, maximum total leverage ratio permitted after May 31, 2014		3.0
Covenant, amount of annual capital expenditures permitted		15,000,000
Covenant, dividend declaration permitted		10,000,000
Iowa Department of Economic Development Loans [Member]
Non interest bearing loans	1,000,000
Number of monthly payments	60 equal monthly payments
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