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Financial Risk Management Objectives - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Aug. 13, 2014
Disclosure Of Financial Instruments [Line Items]          
Unlisted equity securities classified as non-current financial assets-available for sale $ 2,747,000 $ 2,765,000      
Copper costs as a percentage of product cost 80.00% 84.00%      
Provision of allowance for doubtful accounts $ 2,000,000 $ 1,800,000      
Cash and cash equivalents 46,093,000 48,231,000 $ 51,303,000 $ 68,863,000  
Unutilized amounts of bank loans 144,000,000        
Financial liabilities 77,560,000 62,964,000     $ 0
Mortgage of land, buildings, machinery and equipment 8,633,000 8,778,000      
Pledge of other receivables 7,528,000 6,872,000      
Assets and uncalled capital pledged as security $ 1,181,000 $ 842,000      
Top of range [Member]          
Disclosure Of Financial Instruments [Line Items]          
Percentage of financial liabilities bear floating interest rate 45.00%        
Weighted average [Member]          
Disclosure Of Financial Instruments [Line Items]          
Weighted average interest rates on bank loans and overdrafts 2.85% 3.14%      
Subsidiary [Member]          
Disclosure Of Financial Instruments [Line Items]          
Assets and uncalled capital pledged as security $ 25,781,000 $ 27,607,000      
One major customer [Member]          
Disclosure Of Financial Instruments [Line Items]          
Percentage of trade receivables from one customer 22.40% 8.20%      
Interest rate risk [Member]          
Disclosure Of Financial Instruments [Line Items]          
Change of interest rates 0.30% 0.30%      
Change in profit before tax due to change of interest rates $ 113,000 $ 75,000