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Fair Value of Financial Instruments - Summarizes Changes in Fair Value of Level 3 Financial Liabilities (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]      
Fair value, beginning of period $ 11,844 $ 22,420 $ 2,723
Change in fair value of Level 3 financial liabilities (2,496) (9,379) 16,598
Fair value, end of period 5,373 11,844 22,420
2016 Placement Warrants      
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]      
Issuance of Placement Warrants 0 0 0
Fair value of Placement Warrants at exercise (3,457) (1,187) (200)
2017 Placement Warrants      
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]      
Issuance of Placement Warrants 0 0 3,373
Fair value of Placement Warrants at exercise $ (518) $ (10) $ (74)