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Goodwill - Summary of Goodwill (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of reconciliation of changes in goodwill [abstract]    
Beginning balance   $ 50,276
Acquired during the year $ 92,591  
Disposal due to sale   $ (50,276)
Ending balance $ 92,591