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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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Nov. 30, 2019 shares | Dec. 31, 2018 TWD ($) $ / shares | Aug. 31, 2018 TWD ($) shares | Apr. 29, 2018 $ / shares | Dec. 31, 2018 TWD ($) shares | Dec. 31, 2019 TWD ($) shares $ / shares | Dec. 31, 2019 USD ($) shares $ / shares | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($) shares $ / shares | Dec. 31, 2016 TWD ($) shares | Dec. 31, 2007 shares | Dec. 31, 2019 USD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital surplus decreased | $ |  |  | $ 9,530 |  |  |  |  |  |  |  |  |
Compensation cost of employee share options |  |  |  |  |  | $ 871,699 | $ 29,144 | $ 215,648 | $ 354,765 |  |  |
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 |  |  |  |  |  |  |  |  |  |  | 30,000,000 |
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 |  | $ 1,239,456 |  |  | $ 1,239,456 | $ 981,078 |  | $ 1,239,456 | $ 52,388 |  |  | $ 32,801
USISH option plans [member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Valid term of share option plans | 5 years |  |  |  |  | 10 years | 10 years |  |  |  |  |
Capital surplus decreased |  |  |  |  |  | $ 105,785 |  |  |  |  |  | $ 3,537
Options granted |  |  |  |  |  | 23,323,000 | 23,323,000 |  |  |  |  |
USISH option plans [member] | Share Option [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Options granted | 17,167,000 |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |
Share option to purchase of ordinary shares |  |  |  |  |  | 0.5 | 0.5 |  |  |  |  |
Weighted average exercise price of share options | $ / shares |  | $ 68.5 |  | $ 41.0 |  |  |  |  | $ 37.6 |  |  |
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 |  |  |  |  |  |  |  |  | 30,000,000 |  |  |
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 |  |  |  |  |  |  |  |  |  | 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 |  |  | 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) |  |  |  |  |  | $ 69.3 | $ 2.3 |  |  |  |  |
Options granted |  |  |  |  | 131,863,000 |  |  |  |  |  |  |
USISH core employees stock ownership plan [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Options granted | 6,156,000 |  |  |  |  |  |  |  |  |  |  |
USISH core employees stock ownership plan [Member] | Phase One [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Valid term of share option plans | 4.5 years |  |  |  |  |  |  |  |  |  |  |
USISH core employees stock ownership plan [Member] | Phase Two [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Valid term of share option plans | 3.5 years |  |  |  |  |  |  |  |  |  |  |
USISH core employees stock ownership plan [Member] | Phase Three [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Valid term of share option plans | 2.5 years |  |  |  |  |  |  |  |  |  |  |

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