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Income Taxes - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]          
Statutory tax rate 27.60% 19.30% 23.90% 24.00%  
Liability for uncertain tax position $ 0   $ 0   $ 0