Fair Value of Financial Instruments - Schedule of Fair Value of Financial Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	$ 5,373	$ 11,844
Fair Value Measurement on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	5,373	11,844
Fair Value Measurement on Recurring Basis | 2017 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	1,330	7,115
Fair Value Measurement on Recurring Basis | 2016 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	4,043	4,729
Fair Value Measurement on Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	0	0
Fair Value Measurement on Recurring Basis | Level 1 | 2017 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	0	0
Fair Value Measurement on Recurring Basis | Level 1 | 2016 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	0	0
Fair Value Measurement on Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	0	0
Fair Value Measurement on Recurring Basis | Level 2 | 2017 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	0	0
Fair Value Measurement on Recurring Basis | Level 2 | 2016 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	0	0
Fair Value Measurement on Recurring Basis | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	5,373	11,844
Fair Value Measurement on Recurring Basis | Level 3 | 2017 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	1,330	7,115
Fair Value Measurement on Recurring Basis | Level 3 | 2016 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Warrant Liability	$ 4,043	$ 4,729