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Organization and Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Thousands
9 Months Ended
Sep. 30, 2017
USD ($)
Segment
Sep. 30, 2016
USD ($)
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]    
Number of operating segment | Segment 1  
Cash, cash equivalents and marketable securities $ 191,700  
Proceeds from issuance of common stock, net 169,187  
Cash used in operating activities 59,769 $ 80,769
Cowen | Underwritten Public Offering    
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]    
Proceeds from issuance of common stock, net $ 169,000