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Bonds Payable - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2017 USD ($) | Jul. 31, 2015 TWD ($) $ / shares | Jul. 31, 2014 TWD ($) | Sep. 30, 2013 USD ($) $ / shares | Sep. 30, 2017 $ / shares | Dec. 31, 2017 USD ($) $ / shares | Dec. 31, 2017 USD ($) $ / shares | Dec. 31, 2016 $ / shares | Jul. 31, 2015 USD ($) $ / shares | Jul. 31, 2014 USD ($) | Sep. 30, 2013 $ / shares
Unsecured overseas convertible bonds [Member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Bonds face amount |  |  |  | $ 400,000 |  | $ 400,000 | $ 400,000 |  |  |  |
Bonds maturity period |  |  |  | 5 years |  |  |  |  |  |  |
Bonds denomination amount |  |  |  | $ 200 |  |  |  |  |  |  |
Unsecured overseas bonds conversion price | $ / shares |  |  |  | $ 33.085 |  |  |  | $ 28.99 |  |  |
Unsecured overseas bonds fixed exchange rate | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 29.956
Unsecured overseas convertible bonds [Member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Unsecured overseas bonds conversion price | (per share) |  |  |  |  | $ 27.95 | $ 0.94 |  |  |  |  |
Unsecured overseas convertible bonds [Member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Unsecured overseas bonds conversion price | (per share) |  |  |  |  | 28.96 | $ 0.98 |  |  |  |  |
US$400,000 thousand [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Unsecured overseas bonds fixed exchange rate | $ / shares |  |  |  |  | $ 29.956 |  |  |  |  |  |
Common shares trading period |  |  |  |  | 20 days | 20 days | 20 days |  |  |  |
Effective interest rate of debt host contract |  |  | 3.16% |  |  |  |  |  |  |  |
Aggregate fair value of bonds options |  |  | $ 1,667,950 |  |  |  |  |  |  |  |
Early redemption of outstanding bonds | $ 400 |  |  |  |  |  |  |  |  |  |
US$400,000 thousand [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Conversion price percentage |  |  |  | 130.00% |  |  |  |  |  |  |
Aggregate principal amount of bonds redeemed |  |  |  | 90.00% |  |  |  |  |  |  |
US$200,000 thousand [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Bonds face amount |  |  |  |  |  |  |  |  | $ 200,000 |  |
Bonds maturity period |  | 2 years 9 months |  |  |  |  |  |  |  |  |
Bonds denomination amount |  |  |  |  |  |  |  |  | $ 200 |  |
Unsecured overseas bonds conversion price | (per share) |  | $ 54.55 |  |  |  | $ 1.61 | $ 47.76 | $ 49.52 |  |  |
Unsecured overseas bonds fixed exchange rate | $ / shares |  |  |  |  |  |  |  |  | $ 30.928 |  |
Common shares trading period |  |  |  |  |  | 20 days | 20 days |  |  |  |
Effective interest rate of debt host contract |  | 1.58% |  |  |  |  |  |  |  |  |
Aggregate fair value of bonds options |  | $ 214,022 |  |  |  |  |  |  |  |  |
US$200,000 thousand [member] | Bottom of range [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Conversion price percentage |  | 130.00% |  |  |  |  |  |  |  |  |
Aggregate principal amount of bonds redeemed |  | 90.00% |  |  |  |  |  |  |  |  |
US$200,000 thousand [member] | Top of range [member] |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |  |  |  |  |
Common shares trading period |  |  |  |  |  | 30 days | 30 days |  |  |  |
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% |  |  |  |  | 2.125% |  | 2.125% |

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