Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail)

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Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Accounting Policies [Abstract]        
Cash and cash equivalents $ 101,973 $ 51,033    
Restricted cash   13    
Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 101,973 $ 51,046 $ 47,904 $ 9,760