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Financial Instruments - Summary of Maturity Analysis for Derivative Financial Instruments (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2018 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($)
--- | --- | --- | ---
Less than 1 month [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | $ 6,979 | $ 213,624 | $ (40,897)
Less than 1 month [member] | Forward exchange contracts [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Net settled | 67 | 2,040 | (8,820)
Gross settled | 771 | 23,587 | 32,148
Less than 1 month [member] | Forward exchange contracts [member] | Inflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 84,293 | 2,580,194 | 3,711,302
Less than 1 month [member] | Forward exchange contracts [member] | Outflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | (83,522) | (2,556,607) | (3,679,154)
Less than 1 month [member] | Swap contracts [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 6,208 | 190,037 | (73,045)
Less than 1 month [member] | Swap contracts [member] | Inflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 461,830 | 14,136,620 | 12,116,531
Less than 1 month [member] | Swap contracts [member] | Outflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | (455,622) | (13,946,583) | (12,189,576)
1 to 3 months [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 18,619 | 569,944 | (164,400)
1 to 3 months [member] | Forward exchange contracts [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Net settled | 53 | 1,620 |
Gross settled | 188 | 5,764 | 30,458
1 to 3 months [member] | Forward exchange contracts [member] | Inflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 15,240 | 466,489 | 2,169,093
1 to 3 months [member] | Forward exchange contracts [member] | Outflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | (15,052) | (460,725) | (2,138,635)
1 to 3 months [member] | Swap contracts [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 18,431 | 564,180 | (194,858)
1 to 3 months [member] | Swap contracts [member] | Inflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 301,029 | 9,214,500 | 14,434,880
1 to 3 months [member] | Swap contracts [member] | Outflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | (282,598) | (8,650,320) | (14,629,738)
3 months to 1 year [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 51,091 | 1,563,897 | 227,325
3 months to 1 year [member] | Forward exchange contracts [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled |  |  | 3,499
3 months to 1 year [member] | Forward exchange contracts [member] | Inflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled |  |  | 390,379
3 months to 1 year [member] | Forward exchange contracts [member] | Outflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled |  |  | (386,880)
3 months to 1 year [member] | Swap contracts [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 51,091 | 1,563,897 | 223,826
3 months to 1 year [member] | Swap contracts [member] | Inflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | 1,246,662 | 38,160,316 | 36,676,224
3 months to 1 year [member] | Swap contracts [member] | Outflows [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [line items] |  |  |
Gross settled | $ (1,195,571) | $ (36,596,419) | $ (36,452,398)

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- Definition The amount of contractual undiscounted cash flows in relation to contractual amounts to be exchanged in a derivative financial instrument for which gross cash flows are exchanged. [Refer: Derivatives [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph B11D -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_B11D_d&doctype=Appendix&seq=2 -URIDate 2018-03-16 + Details
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- Definition The amount of contractual undiscounted cash flows in relation to net amounts for pay-floating (receive-fixed) interest rate swaps for which net cash flows are exchanged. [Refer: Swap contract [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph B11D -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_B11D_c&doctype=Appendix&seq=2 -URIDate 2018-03-16 + Details
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