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Income Tax - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Income Tax Disclosure [Abstract]          
Effective income tax rate 0.80% 1.40% 0.70% 1.00%  
U.S federal statutory rate 35.00% 35.00% 35.00% 35.00%  
Interest or penalties related to uncertain tax positions $ 0 $ 0 $ 0 $ 0  
Liabilities for interest and potential penalties $ 0   0   $ 0
Increase (decrease) in unrecognized tax benefits     $ 0