Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Details Textual)

v3.19.2
Summary of Significant Accounting Policies (Details Textual)
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 15, 2019
shares
Jun. 02, 2016
USD ($)
Jun. 30, 2019
USD ($)
shares
Jun. 30, 2019
USD ($)
shares
Jun. 30, 2018
USD ($)
shares
Jun. 30, 2019
USD ($)
renewable_identification_number
Jun. 30, 2018
USD ($)
shares
Dec. 31, 2016
Jan. 31, 2019
USD ($)
Jan. 01, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Jun. 30, 2016
USD ($)
Jun. 30, 2014
USD ($)
Business Acquisition [Line Items]                            
Stock Repurchased During Period, Shares | shares         1,296,243,000   1,937,844,000              
Repurchases of shares of common stock         $ 17,220,000   $ 25,048,000              
Restricted cash     $ 3,000,000 $ 3,000,000 0 $ 3,000,000 0       $ 3,000,000      
Biomass-based diesel government incentives       $ 530,000 915,000 998,000 366,200,000              
Shares covered by rebalancing call options               100.00%            
Termination of capped call options (in shares) | shares       625,558                    
Retained earnings     $ (315,227,000) $ (315,227,000)   (315,227,000)         $ (427,244,000)      
Accounting Standards Update 2016-02                            
Business Acquisition [Line Items]                            
Retained earnings                   $ 7,000,000        
December 2017 Program                            
Business Acquisition [Line Items]                            
Repurchases of shares of common stock         17,220,000   25,048,000              
Security repurchase program, amount authorized to be repurchased                       $ 75,000,000    
June 2018 Program                            
Business Acquisition [Line Items]                            
Repurchases of shares of common stock         0   0              
Security repurchase program, amount authorized to be repurchased         75,000,000   75,000,000              
January 2019 Program                            
Business Acquisition [Line Items]                            
Security repurchase program, amount authorized to be repurchased                 $ 75,000,000          
2036 Senior Convertible Notes Repurchases | Convertible Notes                            
Business Acquisition [Line Items]                            
Face amount   $ 152,000,000                     $ 152,000,000  
Interest rate   4.00%                     4.00%  
Convertible Notes Repurchases   $ 147,118,000   $ 0 41,763,000 $ 0 41,763,000              
Principal amount of debt repurchased         24,500,000   24,500,000              
2036 Senior Convertible Notes Repurchases | Convertible Notes | December 2017 Program                            
Business Acquisition [Line Items]                            
Convertible Notes Repurchases         41,763,000   41,763,000              
2036 Senior Convertible Notes Repurchases | Convertible Notes | June 2018 Program                            
Business Acquisition [Line Items]                            
Convertible Notes Repurchases         0   0              
2019 Senior Convertible Notes | Convertible Notes                            
Business Acquisition [Line Items]                            
Face amount                           $ 143,800,000
Interest rate     2.75% 2.75%   2.75%               2.75%
Convertible Notes Repurchases         0   6,689,000              
Principal amount of debt repurchased         0   6,311,000              
Settlement of 2019 Convertible Senior Notes conversion premium (in shares) | shares 1,902,781     1,902,781                    
Termination of capped call options (in shares) | shares     625,558                      
2019 Senior Convertible Notes | Convertible Notes | December 2017 Program                            
Business Acquisition [Line Items]                            
Convertible Notes Repurchases         0   6,689,000              
2019 Senior Convertible Notes | Convertible Notes | June 2018 Program                            
Business Acquisition [Line Items]                            
Convertible Notes Repurchases         $ 0   $ 0              
Minimum                            
Business Acquisition [Line Items]                            
RINs per gallon | renewable_identification_number           1.5                
Allowed RINs per gallon | renewable_identification_number           0                
Maximum                            
Business Acquisition [Line Items]                            
RINs per gallon | renewable_identification_number           1.7                
Allowed RINs per gallon | renewable_identification_number           2.5