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Significant Assets and Liabilities Denominated in Foreign Currencies - Summary of Significant Assets and Liabilities Denominated in Foreign Currencies (Detail) ¥ in Thousands, ¥ in Thousands, $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 TWD ($)	Dec. 31, 2018 TWD ($)	Dec. 31, 2017	Dec. 31, 2019 USD ($)	Dec. 31, 2019 CNY (¥)	Dec. 31, 2019 JPY (¥)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 CNY (¥)	Dec. 31, 2018 JPY (¥)
US Dollar [member] | US dollar equals to New Taiwan dollar [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	$ 123,693,628	$ 114,581,814		$ 4,125,872			$ 3,730,484
Financial liabilities	$ 114,624,313	$ 103,249,185		3,823,359			3,361,523
Exchange Rate	US$1=NT$29.98	US$1=NT$30.715	US$1=NT$29.76
Exchange Rate	US$1=NT$29.98	US$1=NT$30.715	US$1=NT$29.76
US Dollar [member] | US dollar equals to Chinese yuan [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets				1,189,539	¥ 35,662,384		1,299,391	¥ 39,910,801
Financial liabilities				1,211,472	¥ 36,319,926		1,216,654	¥ 37,369,521
Exchange Rate	US$1=CNY6.9762	US$1=CNY6.8632
Exchange Rate	US$1=CNY6.9762	US$1=CNY6.8632
Japanese Yen [Member] | Japanese yen equals to New Taiwan dollar [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	$ 3,833,605	$ 1,227,583				¥ 13,889,872			¥ 4,412,591
Financial liabilities	$ 4,037,478	$ 2,059,131				14,628,543			7,401,621
Exchange Rate	JPY1=NT$0.2760	JPY1=NT$0.2782
Exchange Rate	JPY1=NT$0.2760	JPY1=NT$0.2782
Japanese Yen [Member] | Japanese yen equals to US dollar [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets				212,904		771,392	1,827,400		6,568,657
Financial liabilities				$ 225,197		¥ 815,929	$ 1,957,333		¥ 7,035,704
Exchange Rate	JPY1=US$0.0092	JPY1=US$0.0091
Exchange Rate	JPY1=US$0.0092	JPY1=US$0.0091

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The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Financial instruments, class [member]; Financial liabilities]

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