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Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Income Taxes [Line Items]            
Provision for (benefit from) income taxes $ 2,091 $ 316 $ 300 $ (245) $ (28)  
Effective income tax rate (12.70%)   (1.90%) 0.40% 0.10%  
U.S. statutory tax rate       21.00%   35.00%