Quarterly report pursuant to Section 13 or 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]
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]  
Balance, beginning of period $ 6,091
Change in fair value 4,654
Settlement of financial instruments (3,097)
Balance, end of period $ 7,648