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Income tax expense (Tables) | 12 Months Ended
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Dec. 31, 2020
Text block [abstract] |
Major Components of Income Tax Expense |
| (a) | Components of income tax expense:
|  | Year ended December 31, |
|  | 2018 |  |  | 2019 |  |  | 2020 |
|  | NT$000 |  |  | NT$000 |  |  | NT$000 |
Current income tax: |  |  |  |  |  |  |  |  |  |  |  |
Current income tax on profits for the period |  |  | 326,057 |  |  |  | 408,788 |  |  |  | 636,876 |
Income tax on unappropriated retained earnings |  |  | 28,165 |  |  |  | 74,540 |  |  |  | 105,665 |
Prior year income tax under (over) estimation |  |  | 3,729 |  |  |  | (5,016 | ) |  |  | (133,923 | )
Total current income tax |  |  | 357,951 |  |  |  | 478,312 |  |  |  | 608,618 |
Deferred income tax: |  |  |  |  |  |  |  |  |  |  |  |
Relating to origination and reversal of temporary differences |  |  | 101,441 |  |  |  | 35,367 |  |  |  | (14,237 | )
Impact of change in tax rate |  |  | (2,774 | ) |  |  | — |  |  |  | — |
Total deferred income tax |  |  | 98,667 |  |  |  | 35,367 |  |  |  | (14,237 | )
Income tax expense |  |  | 456,618 |  |  |  | 513,679 |  |  |  | 594,381 |
Deferred Tax Charged to Other Comprehensive Income |
| (b) | The income tax (charge)/credit relating to components of other comprehensive income are as follows:
|  | Year ended December 31, |
|  | 2018 |  |  | 2019 |  |  | 2020 |
|  | NT$000 |  |  | NT$000 |  |  | NT$000 |
Unrealized gain (loss) on valuation of financial assets at fair value through other comprehensive income |  |  | 17,005 |  |  |  | (7,016 | ) |  |  | 34,794 |
Remeasurement of defined benefit obligations |  |  | (11,992 | ) |  |  | 4,183 |  |  |  | (10,398 | )
Impact of change in tax rate |  |  | (887 | ) |  |  | — |  |  |  | — |
|  |  | 4,126 |  |  |  | (2,833 | ) |  |  | 24,396 |
Reconciliation of Income Tax Expense and Accounting Profit Before Income Tax |
| b) | Reconciliation of income tax expense and the accounting profit:
|  | Year ended December 31, |
|  | 2018 |  |  | 2019 |  |  | 2020 |
|  | NT$000 |  |  | NT$000 |  |  | NT$000 |
Tax calculated based on profit before tax and statutory tax rate |  |  | 356,488 |  |  |  | 606,917 |  |  |  | 595,258 |
Effects from adjustments based on regulation |  |  | 81,042 |  |  |  | (162,924 | ) |  |  | 26,974 |
Temporary difference not recognized as deferred tax assets |  |  | (10,951 | ) |  |  | (608 | ) |  |  | (4 | )
Prior year income tax under (over) estimation |  |  | 3,729 |  |  |  | (5,016 | ) |  |  | (133,923 | )
Income tax on unappropriated retained earnings |  |  | 28,165 |  |  |  | 74,540 |  |  |  | 105,665 |
Impact of change in tax rate |  |  | (2,774 | ) |  |  | — |  |  |  | — |
Effect of different tax rates in countries in which the Group operates |  |  | 919 |  |  |  | 770 |  |  |  | 411 |
Income tax expense |  |  | 456,618 |  |  |  | 513,679 |  |  |  | 594,381 |
Details of Deferred Tax Assets (Liabilities) |
| c) | The amounts of deferred tax assets or liabilities resulting from temporary differences and investment tax credits are as follows:
|  | 2018 |
|  | January 1 |  |  | Effects on initial application of IFRS 9 and IFRS 15 |  |  | Recognized in profit or loss |  |  | Recognized in other comprehensive income |  |  | December 31 |
|  | NT$000 |  |  | NT$000 |  |  | NT$000 |  |  | NT$000 |  |  | NT$000 |
Deferred tax assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss on inventories |  |  | 9,132 |  |  |  | (770 | ) |  |  | (1,130 | ) |  |  | — |  |  |  | 7,232 |
Property, plant and equipment |  |  | 55,494 |  |  |  | — |  |  |  | 8,689 |  |  |  | — |  |  |  | 64,183 |
Provisions |  |  | 21,643 |  |  |  | — |  |  |  | (9,247 | ) |  |  | — |  |  |  | 12,396 |
Deferred revenue |  |  | 39,485 |  |  |  | — |  |  |  | (5,329 | ) |  |  | — |  |  |  | 34,156 |
Net defined benefit liability |  |  | 78,451 |  |  |  | — |  |  |  | 7,889 |  |  |  | 14,403 |  |  |  | 100,743 |
Unrealized exchange losses |  |  | 8,167 |  |  |  | 144 |  |  |  | (4,736 | ) |  |  | — |  |  |  | 3,575 |
Investment tax credit |  |  | — |  |  |  | — |  |  |  | 4,420 |  |  |  | — |  |  |  | 4,420 |
Others |  |  | — |  |  |  | — |  |  |  | 11 |  |  |  | — |  |  |  | 11 |
Total |  |  | 212,372 |  |  |  | (626 | ) |  |  | 567 |  |  |  | 14,403 |  |  |  | 226,716 |
Deferred tax liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  | (174,293 | ) |  |  | — |  |  |  | (107,301 | ) |  |  | — |  |  |  | (281,594 | )
Contract assets |  |  | — |  |  |  | (8,067 | ) |  |  | 8,067 |  |  |  | — |  |  |  | — |
Financial assets at fair value through other comprehensive income |  |  | — |  |  |  | (8,636 | ) |  |  | — |  |  |  | (18,529 | ) |  |  | (27,165 | )
Total |  |  | (174,293 | ) |  |  | (16,703 | ) |  |  | (99,234 | ) |  |  | (18,529 | ) |  |  | (308,759 | )
Information presented on statements of financial position: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  | 212,372 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 226,716 |
Deferred tax liabilities |  |  | (174,293 | ) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (308,759 | )
|  | 2019 |
|  | January 1 |  |  | Recognized in profit or loss |  |  | Recognized in other comprehensive income |  |  | December 31 |
|  | NT$000 |  |  | NT$000 |  |  | NT$000 |  |  | NT$000 |
Deferred tax assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss on inventories |  |  | 7,232 |  |  |  | 5,468 |  |  |  | — |  |  |  | 12,700 |
Property, plant and equipment |  |  | 64,183 |  |  |  | (25,515 | ) |  |  | — |  |  |  | 38,668 |
Provisions |  |  | 12,396 |  |  |  | (6,796 | ) |  |  | — |  |  |  | 5,600 |
Deferred revenue |  |  | 34,156 |  |  |  | (6,506 | ) |  |  | — |  |  |  | 27,650 |
Net defined benefit liability |  |  | 100,743 |  |  |  | (3,948 | ) |  |  | (4,183 | ) |  |  | 92,612 |
Unrealized exchange losses |  |  | 3,575 |  |  |  | 13,721 |  |  |  | — |  |  |  | 17,296 |
Investment tax credit |  |  | 4,420 |  |  |  | (4,420 | ) |  |  | — |  |  |  | — |
Others |  |  | 11 |  |  |  | 15 |  |  |  | — |  |  |  | 26 |
Total |  |  | 226,716 |  |  |  | (27,981 | ) |  |  | (4,183 | ) |  |  | 194,552 |
Deferred tax liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  | (281,594 | ) |  |  | (7,386 | ) |  |  | — |  |  |  | (288,980 | )
Financial assets at fair value through other comprehensive income |  |  | (27,165 | ) |  |  | — |  |  |  | 7,016 |  |  |  | (20,149 | )
Total |  |  | (308,759 | ) |  |  | (7,386 | ) |  |  | 7,016 |  |  |  | (309,129 | )
Information presented on statements of financial position |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  | 226,716 |  |  |  |  |  |  |  |  |  |  |  | 194,552 |
Deferred tax liabilities |  |  | (308,759 | ) |  |  |  |  |  |  |  |  |  |  | (309,129 | )
|  | 2020 |
|  | January 1 |  |  | Recognized in profit or loss |  |  | Recognized in other comprehensive income |  |  | December 31 |
|  | NT$000 |  |  | NT$000 |  |  | NT$000 |  |  | NT$000 |
Deferred tax assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss on inventories |  |  | 12,700 |  |  |  | 3,263 |  |  |  | — |  |  |  | 15,963 |
Property, plant and equipment |  |  | 38,668 |  |  |  | (2,267 | ) |  |  | — |  |  |  | 36,401 |
Provisions |  |  | 5,600 |  |  |  | (2,922 | ) |  |  | — |  |  |  | 2,678 |
Deferred revenue |  |  | 27,650 |  |  |  | (6,506 | ) |  |  | — |  |  |  | 21,144 |
Net defined benefit liability |  |  | 92,612 |  |  |  | (4,089 | ) |  |  | 10,398 |  |  |  | 98,921 |
Unrealized exchange losses |  |  | 17,296 |  |  |  | (7,381 | ) |  |  | — |  |  |  | 9,915 |
Others |  |  | 26 |  |  |  | 643 |  |  |  | — |  |  |  | 669 |
Total |  |  | 194,552 |  |  |  | (19,259 | ) |  |  | 10,398 |  |  |  | 185,691 |
Deferred tax liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  | (288,980 | ) |  |  | 33,496 |  |  |  | — |  |  |  | (255,484 | )
Financial assets at fair value through other comprehensive income |  |  | (20,149 | ) |  |  | — |  |  |  | (34,794 | ) |  |  | (54,943 | )
Total |  |  | (309,129 | ) |  |  | 33,496 |  |  |  | (34,794 | ) |  |  | (310,427 | )
Information presented on statements of financial position |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  | 194,552 |  |  |  |  |  |  |  |  |  |  |  | 185,691 |
Deferred tax liabilities |  |  | (309,129 | ) |  |  |  |  |  |  |  |  |  |  | (310,427 | )

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