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Commitments and Contingencies - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]      
Non-cancelable operating lease expiration month and year 2021-06    
Rent expense $ 5.0 $ 3.6 $ 3.4
Future minimum lease payments under noncancelable operating leases in 2019 4.7    
Future minimum lease payments under noncancelable operating leases in 2020 4.8    
Future minimum lease payments under noncancelable operating leases in 2021 $ 2.5