Quarterly report pursuant to Section 13 or 15(d)

Research and Development Agreements - Schedule of Research and Development Revenues Disaggregated by Location (Detail)

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Research and Development Agreements - Schedule of Research and Development Revenues Disaggregated by Location (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Revenue Recognition [Line Items]    
Research and development revenue $ 231 $ 1,760
JAPAN    
Revenue Recognition [Line Items]    
Research and development revenue 163 1,260
UNITED STATES    
Revenue Recognition [Line Items]    
Research and development revenue $ 68 $ 500