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Long-Term Debt - Summary of Debt Refinancing Costs (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]      
Gross cost at January 1 $ 2.7 $ 2.7  
Capitalized in the year 1.5 0.0  
Written down in the year (2.7) 0.0  
Gross cost 1.5 2.7 $ 2.7
Accumulated amortization,Beginning Balance (1.8) (1.1)  
Amortization in the year (1.0) (0.7) (0.6)
Amortization written down in the year 2.7 0.0  
Accumulated amortization,Ending balance (0.1) (1.8) $ (1.1)
Deferred finance costs, net $ 1.4 $ 0.9