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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Income Taxes [Line Items]        
Effective tax rate (3.10%) 25.40% (2.10%) 20.30%
Net unrecognized tax benefits which would impact effective tax rate if recognized $ 0.5   $ 0.5  
Earliest Tax Year        
Income Taxes [Line Items]        
Open tax year     2013  
Latest Tax Year        
Income Taxes [Line Items]        
Open tax year     2016  
Minimum | Subsidiaries        
Income Taxes [Line Items]        
Effective tax rate     0.00%  
Maximum | Subsidiaries        
Income Taxes [Line Items]        
Effective tax rate     40.00%