Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended			9 Months Ended		12 Months Ended
	May. 31, 2015	Feb. 28, 2015	Aug. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	May. 19, 2015	Feb. 03, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Estimated fair value of principal amount				$ 21,879					$ 25,460
Derivative warrant liability fair value				3,395					3,114
Warrants Issued in 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock shares issued and sold						1,420,250
Warrants Issued In Two Thousand And Fourteen
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock shares issued and sold			1,000,000
Warrants Issued in 2015 | Series C Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock shares issued and sold	430,000
Warrants Issued in 2015 | Series B Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock shares issued and sold		2,216,667
Warrants Issued in 2015 | Series A Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock shares issued and sold		2,216,667
2017 Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Estimated fair value of principal amount				26,108					26,108
Fair Value, Inputs, Level 2 | 2017 Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Estimated fair value of principal amount				21,900					25,500
Fair Value, Inputs, Level 2 | 2022 Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Estimated fair value of principal amount				15,200					19,400
Estimated fair value of the embedded derivatives				0					0
Fair Value, Inputs, Level 3 | Warrants Issued in 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative warrant liability fair value				600					$ 1,400
Fair Value, Inputs, Level 3 | Warrants Issued In Two Thousand And Fourteen
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative warrant liability fair value				300
Fair Value, Inputs, Level 3 | Warrants Issued in 2015 | Series C Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative warrant liability fair value				500			$ 1,200
Fair Value, Inputs, Level 3 | Warrants Issued in 2015 | Series B Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative warrant liability fair value				0				$ 2,500
Fair Value, Inputs, Level 3 | Warrants Issued in 2015 | Series A Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative warrant liability fair value				2,000				$ 1,400
Corn
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Write down of inventory				$ 100	$ 200