Fair Value of Financial Instruments - Schedule of Fair Value of Financial Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	$ 12,835	$ 2,723
2017 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	7,127
2016 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	5,708	2,723
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	0
Level 1 | 2017 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	0
Level 1 | 2016 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	0
Level 2 | 2017 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	0
Level 2 | 2016 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	0	0
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	12,835
Level 3 | 2017 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	7,127
Level 3 | 2016 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	$ 5,708	$ 2,723