Acquisitions - (Details) - USD ($) $ in Thousands			12 Months Ended
	Mar. 15, 2016	Aug. 19, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Cash			$ 3,482	$ 12,720	$ 41,409
Summary of allocations of the purchase price to the fair values of the assets acquired and liabilities assumed at the date of acquisition
Debt			0	0	(5,225)
Bargain purchase gain			$ 0	$ 0	$ 5,358
Sanimax
Business Acquisition [Line Items]
Cash	$ 12,541
Common stock	4,050
Contingent consideration	4,500
Total	21,091
Summary of allocations of the purchase price to the fair values of the assets acquired and liabilities assumed at the date of acquisition
Inventory	1,591
Property, plant and equipment	19,500
Total identifiable assets acquired	21,091
Accrued expenses and other liabilities	0
Net identifiable assets acquired	$ 21,091
Imperium Renewables, Inc.
Business Acquisition [Line Items]
Cash		$ 36,748
Common stock		15,310
Contingent consideration		5,000
Total		57,058
Summary of allocations of the purchase price to the fair values of the assets acquired and liabilities assumed at the date of acquisition
Cash		168
Accounts receivable		8,274
Inventory		18,989
Other current assets		87
Property, plant and equipment		46,476
Intangible assets		2,900
Total identifiable assets acquired		76,894
Accounts payable		(4,828)
Accrued expenses and other liabilities		(942)
Debt		(5,225)
Deferred tax liabilities		(3,483)
Total liabilities assumed		(14,478)
Net identifiable assets acquired		62,416
Bargain purchase gain		5,358
Net assets acquired		$ 57,058