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Detail of Interest and Other Income, Net (Parenthetical) (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Other Income And Expenses [Abstract]    
Miscellaneous (expense) income [1] $ (39) $ 1,650
Milestone payment received   $ 1,500
[1] $1.7 million miscellaneous income for the year ended December 31, 2018 is mainly composed of a $1.5 million milestone payment received under an agreement associated with neuronal nicotinic receptor (“NNR”) assets sold in 2016.