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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Income Tax Examination [Line Items]            
Effective tax benefit rate 27.00%   45.30% 21.60% 45.20%  
U.S. federal statutory rate 35.00%   35.00% 35.00% 35.00%  
Unrecognized tax benefits $ 5.9     $ 5.9   $ 4.8
Accrued interest payable for taxes 0.0     0.0   0.0
Liability for income tax penalties 0.0     0.0   $ 0.0
Excess tax benefit [Member]            
Income Tax Examination [Line Items]            
Other Tax Benefit $ 11.4     $ 23.0    
Ownership Structure Change [Member]            
Income Tax Examination [Line Items]            
Other Tax Benefit   $ 4.3