Fair Value of Financial Instruments - Schedule of Fair Value of Financial Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	$ 15,128	$ 2,723
2017 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	8,384
2016 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	6,744	2,723
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	15,128
Level 3 | 2017 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	8,384
Level 3 | 2016 Placement Warrants Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Placement Warrants Liability	$ 6,744	$ 2,723