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Income Taxes - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Income Taxes [Line Items]      
Effective income tax rate 30.10% 25.40%  
Reduction in corporate tax rate 21.00%   35.00%
Adjustment to income tax expense $ 5,400,000    
Minimum [Member]      
Income Taxes [Line Items]      
Reasonably possible decrease in unrecognized tax benefits 2,000,000    
Maximum [Member]      
Income Taxes [Line Items]      
Reasonably possible decrease in unrecognized tax benefits $ 22,000,000