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Share-based Payment Arrangements - Additional Information (Detail) $ / shares in Units, $ / shares in Units, shares in Thousands, $ in Thousands, $ in Thousands | 12 Months Ended |
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Dec. 31, 2017 TWD ($) yr $ / shares | Dec. 31, 2017 USD ($) $ / shares | Dec. 31, 2016 TWD ($) yr $ / shares shares | Dec. 31, 2016 USD ($) shares | Dec. 31, 2015 TWD ($) $ / shares | Dec. 31, 2007 shares | Dec. 31, 2017 USD ($) yr
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |
Compensation cost of employee share options | $ 438,765 | $ 14,803 | $ 470,788 |  | $ 133,496 |  |
USISH option plans [member] |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |
Valid term of share option plans | 10 years | 10 years |  |  |  |  |
Remaining contractual life of share options | yr | 7.9 |  | 8.9 |  |  |  | 7.9
USIE option plans [member] |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |
Capital surplus decreased | $ 52,388 |  | $ 444,320 |  |  |  | $ 1,767
Incremental fair value granted, modified share-based payment arrangements | $ |  |  |  |  | $ 13,721 |  |
ASE Inc. option plans [member] |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |
Valid term of share option plans | 10 years | 10 years |  |  |  |  |
Weighted average exercise price of share options | (per share) | $ 37.60 | $ 1.27 | $ 36.20 |  | $ 38.80 |  |
Reclassification from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $ 47,087 | $ 1,589 |  |  |  |  |
ASE Mauritius Inc. option plan [member] |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |
Valid term of share option plans | 10 years | 10 years |  |  |  |  |
Number of shares granted |  |  |  |  |  | 30,000 |
Reclassification from non-controlling interest to capital surplus arising from expired employee share options | $ 159,200 | $ 5,371 |  |  |  |  |
New shares reserved for subscription by employees under cash capital increase [member] |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |
Options granted to employees to purchase newly issued shares, percentage |  |  | 10.00% | 10.00% |  |  |
Employee benefits expense and capital surplus arising from exercised employee share option |  |  | $ 84,000 | $ 2,834 |  |  |
Number of shares has not been exercised |  |  | 4,836 | 4,836 |  |  |
Amount reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options |  |  | $ 13,541 | $ 457 |  |  |

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- Definition Amount reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options. + References No definition available. + Details
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- Definition Number of share options not exercised in share based payment arrangement. + References No definition available. + Details
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- Definition Reclassification from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options. + References No definition available. + Details
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- Definition Reclassification from non-controlling interest to capital surplus arising from expired employee share options. + References No definition available. + Details
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- Definition The description of the maximum term of options granted for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 45 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_a&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The difference, for modified share-based payment arrangements, between the fair value of the modified equity instrument and that of the original equity instrument, both estimated as at the date of the modification. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 47 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_c_ii&doctype=Standard -URIDate 2017-03-09 + Details
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