Summary of Significant Accounting Policies (Details Textual)	3 Months Ended			6 Months Ended		12 Months Ended		13 Months Ended
	Jun. 30, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) renewable_identification_number	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016	Jun. 30, 2018 USD ($)	Jun. 30, 2016 USD ($)	Jun. 02, 2016 USD ($)
Business Acquisition [Line Items]
Accounts receivable, net	$ 91,248,000	$ 90,648,000		$ 91,248,000		$ 90,648,000		$ 91,248,000
Biomass-based diesel government incentives	$ 915,000		$ 10,821,000	366,200,000	$ 27,762,000
Estimated impaired fixed assets								2,671,000
Estimated insurance recoveries								12,454,000
Payment of business interruption								9,484,000
Shares covered by rebalancing call options							100.00%
Security repurchase program, amount authorized to be repurchased		75,000,000				75,000,000
Security repurchase program, shares repurchased (in shares) | shares	1,937,844
Security repurchase program, value of shares repurchased	$ 25,048,000
Non-cash tax benefit due to Tax Cuts and Jobs Act		13,712,000
2036 Convertible Notes | Convertible Notes
Business Acquisition [Line Items]
Face amount									$ 152,000,000	$ 152,000,000
Interest rate									4.00%	4.00%
Fair value of embedded conversion option						45,933,000
Tax impact of convertible conversion liability reclassification						18,025,000
Cash paid for debt buyback	41,763,000			41,763,000				41,763,000		$ 147,118,000
Principal amount of debt repurchased	24,500,000			24,500,000
2019 Convertible Notes | Convertible Notes
Business Acquisition [Line Items]
Cash paid for debt buyback	$ 6,689,000			6,689,000				$ 6,689,000
Principal amount of debt repurchased				$ 6,311,000
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
Federal goverment | Biodiesel Mixture Excise Tax Credit
Business Acquisition [Line Items]
Accounts receivable, net		365,155,000				365,155,000
Biomass-based diesel government incentives				$ 364,927,000
Customers | Biodiesel Mixture Excise Tax Credit
Business Acquisition [Line Items]
Accounts receivable, net		$ 16,688,000				$ 16,688,000
Biomass-based diesel government incentives				$ 12,062,000