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Property and Equipment, Net - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Leasehold Improvements    
Property Plant And Equipment [Line Items]    
Lessor-paid tenant improvements $ 6.6 $ 1.3
Construction in Progress    
Property Plant And Equipment [Line Items]    
Lessor-paid tenant improvements   $ 5.0
Laboratory Equipment    
Property Plant And Equipment [Line Items]    
Minimum percentage of fair value on present value of expected payments 90.00% 90.00%
Assets under capital lease $ 1.3 $ 1.4
Accumulated depreciation of capital lease $ 0.9 $ 0.2