Segment Data and Foreign Operations (Details)
$ in Thousands
 3 Months Ended 9 Months Ended
May 31, 2016
USD ($)
Nov. 30, 2015
USD ($)
May 31, 2015
USD ($)
May 31, 2016
USD ($)
segment
May 31, 2015
USD ($)
Aug. 31, 2015
USD ($)
Segment data            
Number of operating segments | segment       2    
Revenue $ 64,236   $ 64,898 $ 176,638 $ 173,135  
Income before income taxes 12,466   11,863 34,855 28,888  
Total assets 263,232     263,232   $ 257,897
Interest 284   266 794 810  
Depreciation       4,282 4,238  
Amortization       5,774 4,940  
Cost of sale of inventory step-up     16   65  
Gain on sale of business       1,031    
Asset Impairment Charges       365    
Specialty chemical intermediates product line            
Segment data            
Other Expenses         584  
RodPack Business            
Segment data            
Gain on sale of business       1,031    
Asset Impairment Charges   $ 365        
Industrial Materials            
Segment data            
Revenue 47,185   47,288 134,253 130,013  
Income before income taxes 14,191   13,129 40,391 35,957  
Total assets 139,257     139,257   146,870
Interest 213   235 595 690  
Depreciation 1,007   959 2,952 2,912  
Amortization 1,587   1,647 4,716 3,700  
Construction Materials            
Segment data            
Revenue 17,051   17,610 42,385 43,122  
Income before income taxes 5,662   5,586 14,785 12,051  
Total assets 43,060     43,060   48,016
Interest 71   31 199 120  
Depreciation 240   326 764 895  
Amortization 351   409 1,058 1,240  
Reportable segments            
Segment data            
Income before income taxes 19,853   18,715 55,176 48,008  
Total assets 182,317     182,317   194,886
Corporate and common costs            
Segment data            
Income before income taxes (7,387)   $ (6,852) (20,321) $ (19,120)  
Total assets $ 80,915     $ 80,915   $ 63,011