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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2018
Income Tax Contingency [Line Items]            
Income tax expense (benefit)   $ (28.4) $ 6.2 $ (22.8) $ 11.4  
Income tax expense benefit excluding change in enacted tax rate   $ 4.2   $ 9.8    
Approximate rate on pre-tax income     51.20%   70.80%  
Effective income tax rate continuing operations excluding change in enacted tax rate   113.50%   10.70%    
Tax Act [Member]            
Income Tax Contingency [Line Items]            
Income tax (benefit) due to revaluing of deferred tax liabilities   $ (32.6)        
U.S. federal statutory rate       35.00%    
Tax Act [Member] | Scenario, Forecast            
Income Tax Contingency [Line Items]            
Blended Corporate Tax Rate           28.00%
Tax Act [Member] | Subsequent Event [Member]            
Income Tax Contingency [Line Items]            
U.S. federal statutory rate 21.00%