Fair Value Measurements - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended					9 Months Ended					9 Months Ended				3 Months Ended	9 Months Ended
	Aug. 31, 2014	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Principal Amount of Term Loans	Dec. 31, 2013 Principal Amount of Term Loans	Sep. 30, 2014 Convertible 2017 Notes	Dec. 31, 2013 Convertible 2017 Notes	Sep. 30, 2014 Convertible 2017 Notes Principal Amount of Term Loans	Sep. 30, 2014 2022 Notes	Dec. 31, 2013 2022 Notes	Jul. 31, 2012 2022 Notes	Sep. 30, 2014 Two Thousand Fourteen Amendment	Sep. 30, 2014 Two Thousand Fourteen Amendment Secured Debt	Dec. 31, 2013 Fair Value, Inputs, Level 1	Sep. 30, 2014 Fair Value, Inputs, Level 2 Warrants Issued in 2013	Sep. 30, 2014 Fair Value, Inputs, Level 2 Warrants Issued in 2014	Sep. 30, 2013 Corn	Sep. 30, 2013 Corn
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Write down of inventory		$ 200,000	$ 200,000															$ 600,000	$ 600,000
Secured debt											26,900,000		1,000,000
Amortization period of debt issuance cost										5 years				36 months
Debt instrument maturity date									Mar. 15, 2017	Jul. 01, 2022				May 31, 2017
Debt instrument, stated interest rate												7.50%		9.00%
Estimated fair value of principal amount		25,564,000	25,564,000		0	0	26,108,000	0	25,564,000	18,900,000	15,900,000
Estimated fair value of the embedded derivatives		0	0	3,500,000
Common stock shares issued and sold	15,000,000			21,303,750
Derivative warrant liability fair value		$ 2,877,000	$ 2,877,000	$ 7,243,000											$ 7,200,000	$ 1,300,000	$ 1,600,000