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Investments Accounted For Using Equity Method - Additional Information (Detail) $ in Millions, $ in Millions |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Apr. 30, 2015 TWD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Impairment loss on investments accounted for using equity method |  |  |  | $ 0.0 | $ 0 | $ 0.0 | $ 8.0
Huada Digital Corporation ("HDD") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Disposal loss of investments |  |  |  |  |  | 0.4 |
Chunghwa Benefit One Co., Ltd. ("CBO") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Disposal loss of investments |  |  |  | $ 0.2 |  |  |
KingwayTek Technology Co., Ltd. ("KWT") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Gain on disposal of investments |  |  |  |  |  |  | 7.0
Dian Zuan Integrating Marketing Co., Ltd. ("DZIM") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Ownership interest in associates | 22.00% | 26.00% |  |  |  |  |
Click Force Co., Ltd. ("CF") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Investments in cash in associates |  |  | $ 6.0 |  |  |  |
Ownership interest in associates |  |  |  | 49.00% | 49.00% |  |
Alliance Digital Tech Co., Ltd. ("ADT") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Investments in cash in associates |  |  |  |  |  | $ 30.0 |
Ownership interest in associates |  |  |  |  |  | 14.00% |
Xiamen Sertec Business Technology Co., Ltd. [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Gain on disposal of investments |  |  |  |  |  |  | 1.0
MeWorks LIMITED (HK) ("MeWorks") [Member] |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |
Impairment loss on investments accounted for using equity method |  |  |  |  |  |  | $ 8.0

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