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Changes in Carrying Amount of Goodwill (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Goodwill [Line Items]    
Goodwill, Beginning Balance $ 379,737 $ 378,310
Foreign currency translation adjustment 2,992 1,427
Goodwill, Ending Balance $ 382,729 $ 379,737