Annual report pursuant to Section 13 and 15(d)

Capital Structure - Summary of Common Stock Reserved for Future Issuance (Detail)

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Capital Structure - Summary of Common Stock Reserved for Future Issuance (Detail) - shares
Dec. 31, 2017
Dec. 31, 2016
Class of Stock [Line Items]    
Common Stock reserved for future issuance 42,470,254 31,906,521
Stock Options [Member]    
Class of Stock [Line Items]    
Common Stock reserved for future issuance 6,200,151 4,691,746
Warrants [Member]    
Class of Stock [Line Items]    
Common Stock reserved for future issuance 36,270,103 27,214,775