Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Reconciliation of Level 3 Measurement of Company's Primary Warrant (Detail)

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Summary of Significant Accounting Policies - Reconciliation of Level 3 Measurement of Company's Primary Warrant (Detail) - Warrant [Member]
$ in Thousands
9 Months Ended
Sep. 30, 2017
USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Beginning, Balance $ 7,114
Less: Change in fair value of warrant liability $ (7,114)