Annual report pursuant to Section 13 and 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
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Revenue Recognition [Line Items]    
Total Research and Development Revenue $ 7,283 $ 2,408
JAPAN    
Revenue Recognition [Line Items]    
Total Research and Development Revenue 7,087 1,908
UNITED STATES    
Revenue Recognition [Line Items]    
Total Research and Development Revenue $ 196 $ 500