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Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands, $ in Thousands | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2018 USD ($) | Jun. 30, 2018 TWD ($) | Dec. 31, 2018 $ / shares shares | Dec. 31, 2017 shares | Oct. 13, 2017 shares | Jul. 13, 2017 shares
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Share price | $ / shares |  |  | $ 10 |  |  |
Shares included in authorized shares not yet completed share registration process |  |  |  | 500,000,000 |  |
Number of ordinary shares issued |  |  |  |  | 323,094,000 | 101,164,000
Number of shares represented by each ADS |  |  | 2 | 2 |  |
Distribution of cash from capital surplus arising from issuance of ordinary shares | $ 352,695 | $ 10,795,980 |  |  |  |
Percentage of legal reserve |  |  | 10.00% |  |  |
Percentage of legal reserve on share capital |  |  | 25.00% |  |  |
American depository shares (ADs) [member] |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Number of shares represented by each ADS |  |  | 2 |  |  |
Number of shares outstanding |  |  | 140,042,000 | 115,261,000 |  |
Ordinary shares [member] |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Number of shares outstanding |  |  | 280,085,000 | 576,305,000 |  |
Cash capital increase [member] |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Share price | $ / shares |  |  | $ 34.3 |  |  |
Number of ordinary shares issued |  |  | 300,000,000 |  |  |
A.S.E. Holding Limited [member] |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Proportion of ownership interest in subsidiary |  |  | 100.00% | 100.00% |  |
Number of ordinary shares exchanged from ASE Holding |  |  | 0.5 |  |  |
Repurchase of ordinary shares |  |  | 1,852,000 |  |  |
Repurchase of ordinary shares, price per share | $ / shares |  |  | $ 38.5 |  |  |
Treasury shares canceled |  |  | 121,852,000 |  |  |
Converted bonds [member] |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Ordinary shares issued under conversion of Bonds |  |  | 424,258,000 |  |  |
Top of range [member] |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |
Percentage of cash dividend on dividend distribution |  |  | 30.00% |  |  |

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