Annual report pursuant to Section 13 and 15(d)

Debt - (Details Textual)

v3.7.0.1
Debt - (Details Textual)
1 Months Ended 3 Months Ended 12 Months Ended
Jun. 02, 2016
USD ($)
$ / shares
Oct. 31, 2015
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
shares
Jul. 31, 2015
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Mar. 16, 2016
USD ($)
Short-term Debt [Line Items]                      
Convertible debt conversion liability               $ 27,100,000 $ 0    
Change in fair value of convertible debt conversion liability               13,045,000 0 $ 0  
Notes payable               217,891,000 256,562,000    
Gain on debt extinguishment               2,331,000 0 $ 0  
Wells Fargo Revolver                      
Short-term Debt [Line Items]                      
Additional increase in maximum borrowing capacity           $ 150,000,000 $ 60,000,000 150,000,000      
Line of credit facility limitation amount     $ 50,000,000     50,000,000   $ 40,000,000      
Debt instrument, variable rate minimum               0.00%      
Percentage required of total current revolving loan commitments               10.00%      
Amount required of total current revolving loan commitments               $ 15,000,000      
Wells Fargo Revolver | Minimum                      
Short-term Debt [Line Items]                      
LIBOR rate margin               1.75%      
Fixed charge coverage ratio               100.00%      
Wells Fargo Revolver | Maximum                      
Short-term Debt [Line Items]                      
LIBOR rate margin               2.25%      
Fixed charge coverage ratio               150.00%      
Reg Danville Term Loan                      
Short-term Debt [Line Items]                      
Face amount   $ 12,000,000                  
Debt instrument term   3 years                  
Monthly principal payment   $ 212,000                  
Notes payable               $ 8,163,000 0    
REG Grays Harbor Term Loan                      
Short-term Debt [Line Items]                      
Basis spread on variable rate         3.50%            
Notes payable               $ 9,273,000 $ 5,225,000    
Debt instrument, maximum borrowing capacity         $ 10,000,000.0            
Line of credit         $ 5,000,000            
Interest rate during the period               4.30%      
REG Grays Harbor Term Loan | Minimum                      
Short-term Debt [Line Items]                      
Interest rate               3.50%      
Bankers Trust Company                      
Short-term Debt [Line Items]                      
Line of credit                     $ 30,000,000
Gulf Opportunity Zone Bonds                      
Short-term Debt [Line Items]                      
Face amount               $ 100,000,000      
Collateral amount, certificate of deposit securing obligations               101,315,000      
2.75% Convertible Senior Notes | 2036 Convertible Notes                      
Short-term Debt [Line Items]                      
Face amount $ 152,000,000     $ 152,000,000     $ 152,000,000        
Interest rate 4.00%     4.00%     4.00%        
Percentage of convertible senior notes principal required for repurchase 100.00%                    
Initial conversion rate 92.8074                    
Initial conversion price (in dollars per share) | $ / shares $ 10.78                    
Net proceeds from debt issuance $ 147,118,000                    
Fees and offering expenses 4,882,000                    
Convertible debt conversion liability 40,145,000             27,100,000      
Change in fair value of convertible debt conversion liability               13,045,000      
Notes payable 111,855,000                    
Debt discount $ 40,145,000                    
Effective interest rate 2.45%                    
Proceeds from offering costs used to repurchase shares of Common Stock       $ 35,101,000              
Share repurchase program, shares repurchased (in shares) | shares       4,060,323              
2.75% Convertible Senior Notes | 2019 Convertible Notes                      
Short-term Debt [Line Items]                      
Net proceeds from debt issuance     5,584,000 $ 61,954,000   $ 5,584,000 $ 61,954,000 5,584,000      
Principal amount of debt repurchased     $ 6,000,000 $ 63,912,000       6,000,000      
Gain on debt extinguishment               $ 2,331,000      
LIBOR | Reg Danville Term Loan                      
Short-term Debt [Line Items]                      
Basis spread on variable rate   4.00%           4.00%      
Prime Rate | REG Grays Harbor Term Loan                      
Short-term Debt [Line Items]                      
Basis spread on variable rate         0.25%     0.25%