Debt - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended				1 Months Ended	12 Months Ended						12 Months Ended		3 Months Ended	12 Months Ended
	Jul. 31, 2012	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010	Aug. 31, 2010 Loss on Interest Rate Swap Termination [Member]	Jul. 31, 2012 2012 Agreement [Member]	Aug. 31, 2012 2012 Agreement [Member]	Aug. 31, 2012 2012 Agreement [Member] Two Consecutive Quarters [Member]	Aug. 31, 2012 2012 Agreement [Member] Maximum [Member]	Aug. 31, 2012 2012 Agreement [Member] Maximum [Member] Scenario, Forecast [Member]	Aug. 31, 2012 2012 Agreement [Member] Minimum [Member]	Apr. 07, 2010 2010 Agreement [Member]	Aug. 30, 2010 2010 Agreement [Member] Loss on extinguishment of debt [Member]	Aug. 30, 2010 2010 Agreement [Member] Loss on Interest Rate Swap Termination [Member]	Nov. 30, 2009 Iowa Department Of Economic Development loans [Member]	Aug. 31, 2010 Iowa Department Of Economic Development loans [Member] SecurityLoan	Aug. 31, 2012 Iowa Department Of Economic Development loans [Member]
Proceeds from the issuance of preferred stock				$ 40,000,000
Maximum borrowing amount under amended and restated credit agreement						130,000,000						60,000,000
Scheduled principal payment						0
Line of credit, expiration date	Jul. 09, 2017
Line of credit, amount outstanding							82,600,000
Debt Instrument, Description of Variable Rate Basis over LIBOR (in percentage)									4.00%		2.00%
Convenant, total leverage ratio								2.50		3.75
Convenant, total funded debt ratio year two										3.50
Convenant, total funded debt ratio year three										3.25
Convenant, total funded debt ratio after year three									3.0
Convenant, fixed coverage ratio											1.35
Covenant, amount of annual capital expenditures permitted		14,146,000	8,295,000	5,980,000					15,000,000
Covenant, dividend declaration permitted									10,000,000
Dividend declared, Percentage of cash flow							50.00%
Unamortized transaction fees					1,562,000								1,000,000	1,600,000
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
Capital lease obligations		423,000	490,000
Current portion of capital leases		$ 300,000