Quarterly report pursuant to Section 13 or 15(d)

Income Taxes - Additional Information (Detail)

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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Tax Contingency [Line Items]      
Effective corporate income tax rate 21.00%   35.00%
Deferred tax assets, valuation allowance $ 10.8 $ 5.4  
Cumulative adjusted pre-tax book loss 5.4    
Increase to the valuation allowance amount $ 5.4    
Domestic Tax Authority [Member]      
Income Tax Contingency [Line Items]      
Net operating loss carryforwards for federal income tax purpose   $ 148.1  
Beginning year of expiry for net operating loss carry forwards   2021  
Ending year of expiry for net operating loss carryforwards   2038  
State and Local Jurisdiction [Member]      
Income Tax Contingency [Line Items]      
Net operating loss carryforwards for federal income tax purpose   $ 783.8  
Beginning year of expiry for net operating loss carry forwards   2019  
Ending year of expiry for net operating loss carryforwards   2038