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Financial Instruments at Fair Value Through Profit or Loss - Outstanding Forward Exchange Contracts Not Designated for Hedge (Detail) - Forward exchange contracts [Member]	12 Months Ended
	Dec. 31, 2017 TWD ($)	Dec. 31, 2016 TWD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 EUR (€)
EUR [Member]
Disclosure of detailed information about financial instruments [Line Items]
Currency	EUR/NT$	EUR/NT$
Maturity Period	2018.03-06	2017.03
Contract Amount	$ 69,000,000	$ 167,000,000		€ 2,000,000		€ 5,000,000
USD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Currency	US$/NT$	US$/NT$
Maturity Period	2018.01	2017.01
Contract Amount	$ 125,000,000	$ 55,000,000	$ 4,000,000		$ 2,000,000

X

- Definition

Derivative contract, cross currency.

+ References

No definition available.

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- Definition

Description of derivative financial instruments maturity period.

+ References

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+ Details

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Details

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- Details

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