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Operating Lease Arrangements - Additional Information (Detail) $ in Thousands, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Lease and sublease payments recognised as expense [abstract] |  |  |  |
Operating lease expiration | 2018 to 2023 | 2018 to 2023 |  |
Rental expense | $ 1,193,477 | $ 40,266 | $ 1,411,533 | $ 1,390,821

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- Definition Description of operating lease expiration. + References No definition available. + Details
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Namespace Prefix: | asx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of payments on leases and subleases recognised as an expense by the lessee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2019-01-01 -Name IAS -Number 17 -IssueDate 2017-01-01 -Paragraph 35 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=17&date=2017-03-02&anchor=para_35_c&doctype=Standard&book=B -URIDate 2017-03-09 + Details
Name: | ifrs-full_LeaseAndSubleasePaymentsRecognisedAsExpense
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | ifrs-full_LeaseAndSubleasePaymentsRecognisedAsExpenseAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration