Quarterly report pursuant to Section 13 or 15(d)

Income Taxes - Additional Information (Detail)

v3.10.0.1
Income Taxes - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]          
Liability for unrecognized tax benefit, including related estimates of penalties and interest $ 0 $ 0 $ 0 $ 0  
Income tax provision (benefit) $ 49,000 $ 35,000 $ 91,000 $ 111,000  
Projected annual effective tax rate 0.50% 0.80% 0.60% 0.90%  
Statutory tax rate     21.00%   34.00%