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 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Revenue Recognition [Line Items]        
Total research and development revenue $ 5,211 $ 944 $ 11,624 $ 1,175
JAPAN        
Revenue Recognition [Line Items]        
Total research and development revenue 5,211 932 11,624 1,095
UNITED STATES        
Revenue Recognition [Line Items]        
Total research and development revenue $ 0 $ 12 $ 0 $ 80