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Financial Instruments - Financial Instruments not Carried at Fair Value but which Require Fair Value Disclosure (Detail) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Fair Value Disclosures [Abstract]        
Cash, cash equivalents and restricted cash, Carrying amount $ 52.3 $ 94.3    
Variable rate term loan, Carrying amount 335.9 338.0    
Common stockholders' equity, Carrying amount 395.0 461.9 $ 781.1 $ 935.1
Cash, cash equivalents and restricted cash, Fair value 52.3 94.3    
Variable rate term loan, Fair value 334.6 309.5    
Common stockholders' equity, Fair value $ 1,383.8 $ 653.6