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Basis of Presentation and Summary of Significant Accounting Policies - Income Taxes (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Basis of Presentation and Summary of Significant Accounting Policies        
Effective corporate income tax rate   35.00% 35.00% 35.00%
Estimate reduce value of deferred tax asset   $ (0.6)    
Scenario, Forecast        
Basis of Presentation and Summary of Significant Accounting Policies        
Effective corporate income tax rate 21.00%