Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Schedule of Changes in Fair Value of Liabilities (Detail)

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Summary of Significant Accounting Policies - Schedule of Changes in Fair Value of Liabilities (Detail) - Level 3 [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Balance, beginning of period $ 6,091 $ 1,145
Change in fair value 3,710 5,773
Settlement of financial instruments (9,379) (827)
Extinguishment of financial instruments $ (422)  
Balance, end of period   $ 6,091