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Share-based Payment Arrangements - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands | 1 Months Ended | 4 Months Ended | 8 Months Ended | 12 Months Ended |  |
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Aug. 31, 2018 USD ($) shares | Apr. 29, 2018 $ / shares | Apr. 29, 2018 $ / shares | Dec. 31, 2018 USD ($) yr $ / shares | Dec. 31, 2018 USD ($) yr $ / shares | Dec. 31, 2018 USD ($) yr shares | Dec. 31, 2018 TWD ($) shares | Dec. 31, 2017 TWD ($) yr $ / shares | Dec. 31, 2016 TWD ($) $ / shares shares | Dec. 31, 2007 shares | Dec. 31, 2018 TWD ($) yr | Aug. 31, 2018 TWD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital surplus decreased | $ 311 |  |  |  |  |  |  |  |  |  |  | $ 9,530
Compensation cost of employee share options |  |  |  |  |  | $ 7,045 | $ 215,648 | $ 354,765 | $ 470,788 |  |  |
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 | shares |  |  |  |  |  |  |  |  |  | 30,000,000 |  |
Reclassification from non-controlling interest to capital surplus arising from expired employee share options | $ |  |  |  |  |  |  | $ 159,200 |  |  |  |  |
USIE option plans [member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital surplus decreased |  |  |  | $ 40,492 | $ 40,492 | $ 40,492 |  | $ 52,388 |  |  | $ 1,239,456 |
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 |  |  |  | 6.9 | 6.9 | 6.9 |  | 7.9 |  |  | 6.9 |
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 |  |  |  |  |
Number of employee share option plans |  |  |  |  |  | 5 | 5 |  |  |  |  |
Share option to purchase of ordinary shares | shares |  |  |  |  |  | 0.5 | 0.5 |  |  |  |  |
Weighted average exercise price of share options | (per share) |  | $ 41.0 | $ 1.3 |  |  |  |  | $ 37.6 | $ 36.2 |  |  |
Reclassification from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $ |  |  |  |  |  |  |  | $ 47,087 |  |  |  |
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% |  |  |
Employee benefits expense and capital surplus arising from exercised employee share option | $ |  |  |  |  |  |  |  |  | $ 84,000 |  |  |
Number of shares has not been exercised | shares |  |  |  |  |  |  |  |  | 4,836,000 |  |  |
Amount reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $ |  |  |  |  |  |  |  |  | $ 13,541 |  |  |
The Company Option Plans [member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of shares registered shares | shares | 150,000,000 |  |  |  |  |  |  |  |  |  |  |
Valid term of share option plans |  |  |  |  |  | 10 years | 10 years |  |  |  |  |
Percentage of cash dividend per ordinary share exceeds market price |  |  |  |  |  | 1.50% | 1.50% |  |  |  |  |
Weighted average exercise price of share options | (per share) |  |  |  | $ 68.5 | $ 2.2 |  |  |  |  |  |  |

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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 2018-01-01 -Paragraph 45 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_45_a&doctype=Standard -URIDate 2018-03-16 + Details
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