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Defined Benefit Plans - Summary of Movement in the Fair Value of Plan Assets of the Year (Detail) - Plan assets [member] - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of fair value of plan assets [line items]    
Beginning Balance $ 51,360 $ 44,984
Interest income on plan assets 2,069 1,904
Actuarial gain (loss) (439) (1,196)
Contributions by employer 1,415 1,728
Benefit payments (1,542) (471)
Exchange gain 3,441 4,411
Ending Balance 56,304 51,360
Defined Benefit Pension Plans [member]    
Disclosure of fair value of plan assets [line items]    
Beginning Balance 2,054 1,968
Interest income on plan assets 86 81
Actuarial gain (loss) (55) (32)
Contributions by employer 219  
Benefit payments (57) (26)
Exchange gain 182 63
Ending Balance 2,429 2,054
Supplemental pension plan [member]    
Disclosure of fair value of plan assets [line items]    
Beginning Balance 49,306 43,016
Interest income on plan assets 1,983 1,823
Actuarial gain (loss) (384) (1,164)
Contributions by employer 1,196 1,728
Benefit payments (1,485) (445)
Exchange gain 3,259 4,348
Ending Balance $ 53,875 $ 49,306