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Inventories - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Classes Of Inventories [Abstract]      
Inventories recognized as expense $ 388,079 $ 384,995 $ 356,263
Amount expensed (credited) to cost of sales $ 1,613 $ 532 $ (3,306)