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Financial Instruments at Fair Value Through Profit or Loss - Summary of Outstanding Contracts Not Accounted for Hedge Accounting (Detail) € in Thousands, ¥ in Thousands, ¥ in Thousands, RM in Thousands, $ in Thousands, $ in Thousands, $ in Thousands | 12 Months Ended |  |
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Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2018 CNY (¥) | Dec. 31, 2018 MYR (RM) | Dec. 31, 2018 JPY (¥) | Dec. 31, 2018 SGD ($) | Dec. 31, 2018 EUR (€) | Dec. 31, 2017 TWD ($) | Dec. 31, 2017 CNY (¥) | Dec. 31, 2017 MYR (RM) | Dec. 31, 2017 JPY (¥) | Dec. 31, 2017 SGD ($) | Dec. 31, 2017 EUR (€)
Swap contracts [member] | Sell NT$/buy US$ [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 1,687,400 | $ 1,782,400 | $ 49,570,469 |  |  |  |  |  | $ 53,136,302 |  |  |  |  |
Swap contracts [member] | Sell NT$/buy US$ [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Swap contracts [member] | Sell NT$/buy US$ [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-12 | 2018-12 |  |  |  |  |  |  |  |  |  |  |  |
Swap contracts [member] | Sell US$/buy CNY [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 50,292 | $ 52,948 |  | ¥ 349,800 |  |  |  |  |  | ¥ 349,800 |  |  |  |
Swap contracts [member] | Sell US$/buy JPY [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 54,203 | $ 70,324 |  |  |  | ¥ 6,090,000 |  |  |  |  |  | ¥ 7,870,000 |  |
Swap contracts [member] | Sell US$/buy JPY [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period |  | 2018-02 |  |  |  |  |  |  |  |  |  |  |  |
Swap contracts [member] | Sell US$/buy JPY [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period |  | 2018-03 |  |  |  |  |  |  |  |  |  |  |  |
Swap contracts [member] | Sell US$/buy NT$ [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 208,800 | $ 217,300 | 6,423,242 |  |  |  |  |  | 6,505,767 |  |  |  |  |
Forward exchange contracts [member] | Sell NT$/buy US$ [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period |  | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 80,000 | $ 80,000 | $ 2,453,540 |  |  |  |  |  | 2,389,620 |  |  |  |  |
Forward exchange contracts [member] | Sell NT$/buy US$ [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 |  |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell NT$/buy US$ [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-02 |  |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/buy CNY [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 29,000 | $ 125,000 |  | ¥ 200,108 |  |  |  |  |  | ¥ 828,858 |  |  |  |
Forward exchange contracts [member] | Sell US$/buy CNY [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period |  | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/buy CNY [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period |  | 2018-04 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/buy JPY [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 37,733 | $ 45,517 |  |  |  | ¥ 4,231,754 |  |  |  |  |  | ¥ 5,111,101 |  |
Forward exchange contracts [member] | Sell US$/buy JPY [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/buy JPY [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-02 | 2018-02 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/buy NT$ [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period |  | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount |  | $ 1,000 |  |  |  |  |  |  | $ 30,142 |  |  |  |  |
Forward exchange contracts [member] | Sell US$/Buy EUR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 4,103 | $ 10,674 |  |  |  |  |  | € 3,600 |  |  |  |  |  | € 9,000
Forward exchange contracts [member] | Sell US$/Buy MYR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 14,000 | $ 15,000 |  |  | RM 58,430 |  |  |  |  |  | RM 61,859 |  |  |
Forward exchange contracts [member] | Sell US$/Buy MYR [Member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/Buy MYR [Member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-02 | 2018-03 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/Buy SGD [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount | $ 13,400 | $ 11,300 |  |  |  |  | $ 18,391 |  |  |  |  |  | $ 15,305 |
Forward exchange contracts [member] | Sell US$/Buy SGD [Member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-01 | 2018-01 |  |  |  |  |  |  |  |  |  |  |  |
Forward exchange contracts [member] | Sell US$/Buy SGD [Member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity Period | 2019-02 | 2018-02 |  |  |  |  |  |  |  |  |  |  |  |

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