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Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits [Abstract]    
Balance at January 1 $ 2,878 $ 2,874
Additions based on tax positions related to the current year 2 2
Additions for tax positions of prior years   2
Reductions in prior year tax positions (1)  
Balance at December 31 $ 2,879 $ 2,878