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Share-based Payment Arrangements - Summary of Information About ASE Mauritius Inc. Option Plan (Detail) shares in Thousands | 8 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 $ / shares | Dec. 31, 2019 $ / shares | Dec. 31, 2017 shares $ / shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average exercise price, Beginning balance |  | $ 58.1 |
Weighted average exercise price, Options forfeited | $ 71.5 |  |
ASE Mauritius Inc. option plan [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Number of options, beginning balance | shares |  |  | 28,470
Number of options, forfeited | shares |  |  | (250)
Number of options, expired | shares |  |  | (28,220)
Weighted average exercise price, Beginning balance |  |  | $ 1.7
Weighted average exercise price, Options forfeited |  |  | 1.7
Weighted average exercise price, Options expired |  |  | $ 1.7

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- Definition The number of share options expired in a share-based payment arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2019-01-01 -Paragraph 45 -Subparagraph b -Clause v -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2019-en-r&anchor=para_45_b_v&doctype=Standard -URIDate 2019-03-27 + Details
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