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Share-based Payments Arrangement - CHIEF's Outstanding Stock Options (Detail) - CHIEF Telecom Inc. (CHIEF) [Member] | 12 Months Ended
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Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Granted on October 22, 2015 [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Number of options, Options outstanding at beginning of the year | 1,948 | 2,000 | 0
Number of options, Options granted | 0 | 0 | 2,000
Number of options, Options forfeited | (12) | (52) |
Number of options, Options outstanding at end of the year | 1,936 | 1,948 | 2,000
Number of options, Option exercisable at end of the year | 968 | 0 | 0
Weighted-average exercise price, Options outstanding at beginning of the year | $ 34.40 | $ 43.00 | $ 0
Weighted average exercise price, Options granted | 0 | 0 | 43.00
Weighted average exercise price, Options forfeited | 0 | 0 | 0
Weighted-average exercise price, Options outstanding at end of the year | 34.40 | 34.40 | 43.00
Weighted-average exercise price, Options exercisable at end of the year | $ 34.40 | $ 0 | $ 0
Granted on December 19, 2017 [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Number of options, Options granted | 950 |  |
Number of options, Options outstanding at end of the year | 950 |  |
Number of options, Option exercisable at end of the year | 0 |  |
Weighted average exercise price, Options granted | $ 147.00 |  |
Weighted average exercise price, Options forfeited | 0 |  |
Weighted-average exercise price, Options outstanding at end of the year | 147.00 |  |
Weighted-average exercise price, Options exercisable at end of the year | $ 0 |  |

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