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Property and Equipment - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Property, Plant and Equipment [Line Items]      
Depreciation and amortization $ 12.9 $ 9.4 $ 5.9
Accumulated depreciation 3.1 2.4  
Leasehold Improvements [Member]      
Property, Plant and Equipment [Line Items]      
Capitalized asset retirement costs $ 1.3 $ 1.1