Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Summary of Cash, Cash Equivalents and Short-Term Investments (Detail)

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Fair Value Measurements - Summary of Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Dec. 31, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]        
Cash, amortized cost and estimated fair value $ 3,010      
Cash and cash equivalents, amortized cost and estimated fair value 8,021 $ 15 $ 27 $ 67
Restricted cash, amortized cost and estimated fair value 272      
Money market securities [Member]        
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]        
Cash equivalents, amortized cost and estimated fair value 5,011      
Restricted cash, amortized cost and estimated fair value $ 272