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Income Tax - Additional Information (Detail) - USD ($)
3 Months Ended
Sep. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Mar. 31, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]          
Effective income tax rate   12.00%   0.60%  
Reduction in our valuation allowance due to tax reform   $ 4,000,000      
Interest or penalties related to uncertain tax positions $ 0   $ 0    
Liabilities for interest and potential penalties   0     $ 0
Increase (decrease) in unrecognized tax benefits   $ 0