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Income Taxes - Additional Information (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2018
Sep. 30, 2018
Dec. 31, 2017
Income Taxes [Line Items]          
United States statutory tax rate 24.50% 35.00%     35.00%
Valuation allowance for deferred tax assets or provision for income taxes $ 0       $ 0
Company's effective tax rates (0.10%) (9.60%)      
Scenario, Forecast          
Income Taxes [Line Items]          
United States statutory tax rate     21.00% 24.50%