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Segment Information - Financial Segment Information for Operating Segments (Detail) $ in Thousands, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($)
Revenue |  |  |  |
Revenue | $ 23,011,381 | $ 819,493 | $ 20,337,881 | $ 18,480,027
Operating profit (loss) | 3,566,502 | $ 127,012 | 2,457,119 | 2,099,721
Interest expense | (162,400) |  | (171,075) | (152,416)
Purchase of property, plant and equipment | 4,133,615 |  | 4,896,656 | 4,945,570
Continuing operations [member] |  |  |  |
Revenue |  |  |  |
Revenue | 23,011,381 |  | 20,337,881 | 18,480,027
Operating profit (loss) | 3,566,502 |  | 2,457,119 | 2,099,721
Depreciation expenses | (4,175,519) |  | (3,731,914) | (3,376,579)
Share of profit (loss) of associates | (147,329) |  | (154,926) | (300,101)
Interest income | 27,778 |  | 64,368 | 49,971
Interest expense | (162,400) |  | (171,075) | (152,416)
Purchase of property, plant and equipment | 4,133,615 |  | 4,896,656 | 4,945,570
Continuing operations [member] | External [member] |  |  |  |
Revenue |  |  |  |
Revenue | 23,011,381 |  | 20,337,881 | 18,480,027
Continuing operations [member] | Operating segments [member] | Testing [member] |  |  |  |
Revenue |  |  |  |
Revenue | 5,002,730 |  | 4,257,800 | 4,790,097
Operating profit (loss) | 1,333,682 |  | 709,142 | 1,306,742
Depreciation expenses | (853,829) |  | (802,740) | (769,660)
Purchase of property, plant and equipment | 887,204 |  | 764,105 | 1,563,919
Continuing operations [member] | Operating segments [member] | Testing [member] | External [member] |  |  |  |
Revenue |  |  |  |
Revenue | 5,002,730 |  | 4,257,800 | 4,790,097
Continuing operations [member] | Operating segments [member] | Assembly [member] |  |  |  |
Revenue |  |  |  |
Revenue | 6,001,964 |  | 5,148,877 | 4,679,676
Operating profit (loss) | 67,730 |  | (227,096) | (207,700)
Depreciation expenses | (523,341) |  | (521,311) | (578,205)
Purchase of property, plant and equipment | 803,693 |  | 548,063 | 321,976
Continuing operations [member] | Operating segments [member] | Assembly [member] | External [member] |  |  |  |
Revenue |  |  |  |
Revenue | 6,001,964 |  | 5,148,877 | 4,679,676
Continuing operations [member] | Operating segments [member] | LCDD [member] |  |  |  |
Revenue |  |  |  |
Revenue | 7,023,003 |  | 6,922,205 | 5,694,720
Operating profit (loss) | 1,687,986 |  | 1,740,720 | 1,226,755
Depreciation expenses | (2,213,504) |  | (1,796,951) | (1,400,784)
Purchase of property, plant and equipment | 2,143,401 |  | 3,077,806 | 2,732,141
Continuing operations [member] | Operating segments [member] | LCDD [member] | External [member] |  |  |  |
Revenue |  |  |  |
Revenue | 7,023,003 |  | 6,922,205 | 5,694,720
Continuing operations [member] | Operating segments [member] | Bumping [member] |  |  |  |
Revenue |  |  |  |
Revenue | 4,983,684 |  | 4,008,999 | 3,315,534
Operating profit (loss) | 487,323 |  | 232,404 | (202,497)
Depreciation expenses | (578,890) |  | (604,553) | (627,412)
Purchase of property, plant and equipment | 298,834 |  | 506,635 | 327,251
Continuing operations [member] | Operating segments [member] | Bumping [member] | External [member] |  |  |  |
Revenue |  |  |  |
Revenue | 4,983,684 |  | 4,008,999 | 3,315,534
Continuing operations [member] | Operating segments [member] | Others [member] |  |  |  |
Revenue |  |  |  |
Revenue | 39,646 |  | 32,808 | 35,738
Operating profit (loss) | (10,230) |  | 1,931 | (23,433)
Depreciation expenses | (5,955) |  | (6,359) | (518)
Share of profit (loss) of associates | (320,578) |  | (370,351) | (668,377)
Interest income | 27,778 |  | 64,368 | 49,971
Interest expense | (162,400) |  | (171,075) | (152,416)
Purchase of property, plant and equipment | 483 |  | 47 | 283
Continuing operations [member] | Operating segments [member] | Others [member] | Intersegment [member] |  |  |  |
Revenue |  |  |  |
Revenue | 39,646 |  | 32,808 | 35,738
Continuing operations [member] | Elimination [member] |  |  |  |
Revenue |  |  |  |
Revenue | (39,646) |  | (32,808) | (35,738)
Operating profit (loss) | 11 |  | 18 | (146)
Share of profit (loss) of associates | 173,249 |  | 215,425 | 368,276
Continuing operations [member] | Elimination [member] | Intersegment [member] |  |  |  |
Revenue |  |  |  |
Revenue | $ (39,646) |  | $ (32,808) | $ (35,738)

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