Note 9 - Segment Information (Tables)
 9 Months Ended
Sep. 30, 2016
Notes Tables  
Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block]
   
Three months ended September 30:
    
Nine months ended September 30:
  
   
2016
    
2015
    
2016
    
2015
  
United States
   $ 68,462     $ 106,300     $ 181,677     $ 264,034  
All Foreign Countries
     844       754       2,143       1,705  
Total
   $ 69,306     $ 107,054     $ 183,820     $ 265,739  
Schedule of Segment Reporting Information, by Segment [Table Text Block]
   
Three months ended September 30:
    
Nine months ended September 30:
  
   
2016
    
2015
    
2016
    
2015
  
Revenue
                                
Custom chemicals
   $ 20,455     $ 26,665     $ 60,148     $ 84,621  
Performance chemicals
     3,844       4,942       13,782       13,880  
Chemicals revenue
     24,299       31,607       73,930       98,501  
Biofuels revenue
     45,007       75,447       109,890       167,238  
Total Revenue
   $ 69,306     $ 107,054     $ 183,820     $ 265,739  
                                 
Segment gross profit
                                
Chemicals
   $ 7,853     $ 7,294     $ 22,722     $ 28,159  
Biofuels
     2,466       1,381       6,622       (626 )
Total gross profit
     10,319       8,675       29,344       27,533  
Corporate expenses
     (2,478 )     (2,742 )     (7,598 )     (7,646 )
Income before interest and taxes
     7,841       5,933       21,746       19,887  
Interest and other income
     1,637       1,336       4,446       5,210  
Interest and other expense
     (478 )     (359 )     (1,188 )     (261 )
Benefit/(provision) for income taxes
     3,868       (2,060 )     12,657       (8,062 )
Net income
   $ 12,868     $ 4,850     $ 37,661     $ 16,774