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Related Parties - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Holdco      
Related Party Transaction [Line Items]      
Related party transactions expense recognized on transaction $ 22.4 $ 18.9 $ 14.1
Lanis      
Related Party Transaction [Line Items]      
Related party transactions expense recognized on transaction $ 8.3 $ 7.8 $ 7.3