Reportable Segments and Geographic Information - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment for the results of operations
Net sales	$ 2,158,243	$ 2,041,232	$ 1,387,344
Income (loss) before income taxes	(109,569)	48,981	(160,411)
Depreciation and amortization expense, net	36,936	32,877	25,876
Cash paid for purchases of property, plant and equipment	67,572	60,705	64,477
Goodwill	16,080	16,080
Assets	1,005,596	1,136,603
Corporate and other
Segment for the results of operations
Net sales	212,557	106,572	68,984
Income (loss) before income taxes	(29,217)	984	(13,854)
Depreciation and amortization expense, net	2,167	1,696	1,362
Cash paid for purchases of property, plant and equipment	2,998	2,549	2,436
Assets	386,590	299,825
Operating Segments | Biomass-based Diesel
Segment for the results of operations
Net sales	2,039,982	1,952,361	1,326,452
Income (loss) before income taxes	(63,925)	64,814	(100,152)
Depreciation and amortization expense, net	31,011	29,018	22,799
Cash paid for purchases of property, plant and equipment	60,734	52,952	59,859
Goodwill	0	0
Assets	898,180	1,026,349
Operating Segments | Biomass-based Diesel | REG Germany
Segment for the results of operations
Net sales	171,175	171,358	145,039
Income (loss) before income taxes	(7,544)	5,007	(1,643)
Depreciation and amortization expense, net	2,990	2,849	3,259
Cash paid for purchases of property, plant and equipment	3,241	1,353	1,816
Assets	55,761	51,822
Operating Segments | Services
Segment for the results of operations
Net sales	103,215	87,014	102,731
Income (loss) before income taxes	2,899	2,970	6,323
Depreciation and amortization expense, net	1,092	613	302
Cash paid for purchases of property, plant and equipment	3,826	4,731	1,510
Goodwill	16,080	16,080
Assets	55,581	53,823
Operating Segments | Renewable Chemicals
Segment for the results of operations
Net sales	4,531	2,065	0
Income (loss) before income taxes	(19,326)	(19,787)	(52,728)
Depreciation and amortization expense, net	2,666	1,550	1,413
Cash paid for purchases of property, plant and equipment	14	473	672
Goodwill	0	0
Assets	21,168	22,883
Intersegment revenues
Segment for the results of operations
Net sales	(202,042)	(106,780)	$ (110,823)
Intersegment eliminations
Segment for the results of operations
Assets	$ (355,923)	$ (266,277)