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Financial Risk Management and Fair Values of Financial Instruments - Maturity Profile of Non-derivative Financial Liabilities Based on Contracted Undiscounted Payments (Detail) - TWD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items] |  |  |
Long-term bank loans | $ 8,091,523 | $ 9,549,328 |
Lease liabilities | 1,079,181 | 917,452 | $ 1,184,183
Guarantee deposits | 21,670 | 1,095 |
Total | 9,192,374 | 10,467,875 |
Within 1 year [member] |  |  |
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items] |  |  |
Long-term bank loans | 846,401 | 914,159 |
Lease liabilities | 145,594 | 36,806 |
Total | 991,995 | 950,965 |
1 to 3 years [member] |  |  |
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items] |  |  |
Long-term bank loans | 3,558,597 | 1,786,842 |
Lease liabilities | 160,146 | 60,111 |
Total | 3,718,743 | 1,846,953 |
3 to 5 years [member] |  |  |
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items] |  |  |
Long-term bank loans | 2,198,717 | 6,848,327 |
Lease liabilities | 54,689 | 57,836 |
Total | 2,253,406 | 6,906,163 |
Over 5 years [member] |  |  |
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items] |  |  |
Long-term bank loans | 1,487,808 |  |
Lease liabilities | 718,752 | 762,699 |
Guarantee deposits | 21,670 | 1,095 |
Total | $ 2,228,230 | $ 763,794 |

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