Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail)

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Financial Instruments - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]        
Cash and cash equivalents $ 66,028 $ 79,223    
Restricted cash - short-term 194 194    
Restricted cash - long-term 1,200 1,200    
Total cash, cash equivalents and restricted cash $ 67,422 $ 80,617 $ 61,887 $ 48,162