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Litigation - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Litigation Settlement [Abstract]          
Litigation provisions $ (322) $ (924) $ 1,672 $ 426 $ (11,114)