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Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Tax Disclosure [Abstract]        
U.S. federal statutory income tax rate   21.00% 35.00% 35.00%
Non-cash deferred income tax benefit $ 1,900   $ 1,861