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Bonds Payable - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2017 USD ($) | Jul. 31, 2015 USD ($) | Oct. 31, 2014 USD ($) $ / shares | Oct. 31, 2014 TWD ($) | Jul. 31, 2014 USD ($) | Sep. 30, 2013 USD ($) | Dec. 31, 2017 TWD ($) $ / shares | Dec. 31, 2018 USD ($) | Jul. 31, 2015 TWD ($) $ / shares | Oct. 31, 2014 TWD ($) $ / shares
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Arising from equity component of convertible bonds |  |  |  |  |  |  | $ 214,022 |  |  |
Siliconware Precision Industries Co., Ltd. [member] |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Bonds maturity period |  |  | 5 years | 5 years |  |  |  |  |  |
Bonds face amount |  |  | $ 400,000 |  |  |  |  |  |  |
Outstanding bond |  |  | 148,000 |  |  |  |  |  |  |
Total consideration |  |  | $ 170,434 | $ 5,216,985 |  |  |  |  |  |
Consideration per share | (per share) |  |  | $ 1.67 |  |  |  |  |  |  | $ 51.20
Securities transactions tax |  |  | 0.30% | 0.30% |  |  |  |  |  |
Change in capital surplus |  |  | $ 12,692 |  |  |  |  |  |  | $ 388,491
Unsecured overseas convertible bonds [member] |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Bonds face amount |  |  |  |  |  | $ 400,000 |  |  |  |
Bonds maturity period |  |  |  |  |  | 5 years |  |  |  |
Unsecured overseas bonds conversion right exercised | $ 399,600 |  |  |  |  |  |  |  |  |
Early redeemed the outstanding Bonds | $ 400 |  |  |  |  |  |  |  |  |
Unsecured overseas convertible bonds [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Unsecured overseas bonds conversion price | $ / shares |  |  |  |  |  |  | $ 27.95 |  |  |
Unsecured overseas convertible bonds [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Unsecured overseas bonds conversion price | $ / shares |  |  |  |  |  |  | $ 28.96 |  |  |
US$200,000 thousand [member] |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Bonds face amount |  | $ 200,000 |  |  |  |  |  | $ 200,000 |  |
Bonds maturity period |  | 2 years 9 months |  |  |  |  |  |  |  |
Unsecured overseas bonds fixed exchange rate | $ / shares |  |  |  |  |  |  |  |  | $ 30.928 |
Arising from equity component of convertible bonds |  |  |  |  |  |  |  |  | $ 214,022 |
Secured Overseas Bonds One [member] |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |
Bonds face amount |  |  |  |  | $ 300,000 |  |  |  |  |
Bonds maturity period |  |  |  |  | 3 years |  |  |  |  |
Percentage of ownership interest in subsidiary |  |  |  |  | 100.00% |  |  |  |  |
Annual interest rates of bonds |  |  |  |  | 2.125% |  |  |  |  |

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