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Long-Term Debt - Summary of Debt Refinancing Costs (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]      
Gross cost,Beginning balance $ 1.5 $ 2.6  
Capitalized in the year 1.2 1.5 $ 0.1
Written down in the year 0.0 (2.6)  
Gross cost,Ending Balance 2.7 1.5 2.6
Accumulated amortization,Beginning Balance (0.1) (1.5)  
Amortization in the year (0.4) (1.2)  
Amortization written down in the year 0.0 2.6  
Accumulated amortization,Ending balance (0.5) (0.1) $ (1.5)
Deferred finance costs $ 2.2 $ 1.4