Reportable Segments and Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net revenues	$ 580,150	$ 535,103	$ 1,269,402	$ 953,996
Income (loss) before income taxes	37,685	(32,849)	250,871	(47,688)
Depreciation and amortization expense, net	9,618	8,973	19,111	17,836
Cash paid for purchases of property, plant and equipment	12,358	15,401	29,180	32,037
Goodwill	16,080		16,080		$ 16,080
Assets	1,152,770		1,152,770		1,005,596
Intersegment Revenues
Segment Reporting Information [Line Items]
Net revenues	(33,383)	(58,714)	(84,142)	(91,359)
Assets	(272,478)		(272,478)		(355,923)
Biomass-based Diesel | Segments
Segment Reporting Information [Line Items]
Net revenues	541,774	532,527	1,170,167	922,632
Income (loss) before income taxes	32,394	4,323	247,964	(6,392)
Depreciation and amortization expense, net	8,427	7,830	16,731	15,570
Cash paid for purchases of property, plant and equipment	11,447	13,517	27,049	29,398
Assets	955,055		955,055		898,180
Biomass-based Diesel | Segments | REG Germany
Segment Reporting Information [Line Items]
Net revenues	43,369	41,473	89,725	95,025
Income (loss) before income taxes	(1,078)	(2,092)	(5,689)	(1,332)
Depreciation and amortization expense, net	570	788	1,367	1,474
Cash paid for purchases of property, plant and equipment	288	1,227	701	2,395
Assets	53,768		53,768		55,761
Services
Segment Reporting Information [Line Items]
Goodwill	16,080		16,080		16,080
Services | Segments
Segment Reporting Information [Line Items]
Net revenues	17,523	20,922	52,738	43,755
Income (loss) before income taxes	(267)	(267)	4,757	(377)
Depreciation and amortization expense, net	357	251	685	482
Cash paid for purchases of property, plant and equipment	911	938	1,763	1,520
Assets	61,040		61,040		55,581
Renewable Chemicals | Segments
Segment Reporting Information [Line Items]
Net revenues	1,063	1,002	2,923	1,830
Income (loss) before income taxes	(6,291)	(4,828)	(13,775)	(9,835)
Depreciation and amortization expense, net	394	384	789	769
Cash paid for purchases of property, plant and equipment	0	0	335	7
Assets	19,501		19,501		21,168
Corporate and Other
Segment Reporting Information [Line Items]
Net revenues	53,173	39,366	127,716	77,138
Income (loss) before income taxes	11,849	(32,077)	11,925	(31,084)
Depreciation and amortization expense, net	440	508	906	1,015
Cash paid for purchases of property, plant and equipment	0	$ 946	33	$ 1,112
Assets	$ 389,652		$ 389,652		$ 386,590