Quarterly report pursuant to Section 13 or 15(d)

Research and Development Agreements - Schedule of Contract Assets and Contract Liabilities for Performance Obligations related to Collaboration Agreements (Parenthetical) (Detail)

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Research and Development Agreements - Schedule of Contract Assets and Contract Liabilities for Performance Obligations related to Collaboration Agreements (Parenthetical) (Detail) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Contract With Customer Asset And Liability [Line Items]    
Research and development revenue $ 231,000 $ 1,760,000
Deferred Revenue    
Contract With Customer Asset And Liability [Line Items]    
Research and development revenue $ 163,000