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Income Taxes - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Taxes [Line Items]    
Uncertain tax liabilities $ 0 $ 0
Adjustments for New Accounting Pronouncement    
Income Taxes [Line Items]    
Excess tax benefit $ 5,400,000 $ 5,800,000