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Employee Benefit - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Defined Benefit Plans [Abstract]      
Total charges for defined contribution pension plans $ 1,280 $ 1,237 $ 1,172
Net benefit cost 570 590 $ 551
Employee benefit liability, amount recognized in current liabilities 877 594  
Employee benefit liability, amount recognized in non-current liabilities 7,416 6,058  
Amount of long service leave $ 586 $ 527