Segment Reporting - Segment Wide Reporting Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
May 31, 2014
May 31, 2013
May 31, 2014
May 31, 2013
Aug. 31, 2013
Segment Reporting Information [Line Items]          
Sales $ 119,429 $ 121,719 $ 334,786 $ 349,823  
Income (loss) from operations 4,925 4,275 9,476 10,825  
Total assets 236,628   236,628   224,618
Industrial Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Sales 84,112 93,184 240,539 267,030  
Food Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Sales 35,317 28,535 94,247 82,793  
Industrial Starch [Member] | Industrial Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Sales 39,723 44,572 120,261 132,610  
Ethanol [Member] | Industrial Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Sales 27,952 28,111 72,966 69,710  
By-Products [Member] | Industrial Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Sales 16,437 20,501 47,312 64,710  
Operating Segments [Member] | Industrial Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Income (loss) from operations 1,957 565 (72) 1,500  
Total assets 136,020   136,020   133,120
Operating Segments [Member] | Food Ingredients [Member]
         
Segment Reporting Information [Line Items]          
Income (loss) from operations 6,025 6,206 18,349 17,097  
Total assets 88,423   88,423   68,550
Corporate, Non-Segment [Member]
         
Segment Reporting Information [Line Items]          
Income (loss) from operations (3,057) (2,496) (8,801) (7,772)  
Total assets $ 12,185   $ 12,185   $ 22,948