Borrowings (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Company's borrowings
Total notes payable	$ 32,009	$ 32,731
Variable Interest Entities
Company's borrowings
Total notes payable	4,245	4,313
REG Danville term loan
Company's borrowings
Total notes payable	9,760	10,060
REG Newton term loan
Company's borrowings
Total notes payable	20,783	21,175
Other
Company's borrowings
Total notes payable	$ 1,466	$ 1,496