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Financial Instruments - Summary of Fair Value of Financial Instruments that are Measured at Fair Value on a Recurring Basis (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($)
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Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | $ 5,288,996 | $ 176,830 | $ 7,898,458
Financial assets at FVTOCI | 3,800,465 | 12,706 | 1,597,323
Financial liabilities at FVTPL | 973,571 | 32,550 | 36,655
Investments in equity instruments designated at fair value through other comprehensive income | 755,903 | 25,272 | 580,399
Trade receivables, net | 1,014,872 | 33,931 | 1,016,924
Swap contracts [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 56,561 | 1,891 | 1,557,714
Financial liabilities at FVTPL | 862,581 | 28,839 | 29,058
Forward Exchange Contract [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 104,308 | 3,487 | 32,070
Financial liabilities at FVTPL | 110,990 | 3,711 | 7,597
Quoted ordinary shares [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 3,460,123 | 115,685 | 5,151,255
Open-end mutual funds [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 662,290 | 22,143 | 581,800
Unquoted preferred shares [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Investments in equity instruments designated at fair value through other comprehensive income | 158,718 | 5,306 |
Unquoted preferred shares [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 377,440 | 12,619 | 275,000
Private-placement funds [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 603,718 | 20,184 | 200,123
Private-placement convertible bonds [member] | Hybrid financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL |  |  | 100,496
Unquoted ordinary shares [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets at FVTOCI, Investments in equity instruments |  |  | 540,730
Investments in equity instruments designated at fair value through other comprehensive income | 565,028 | 18,891 |
Limited partnership [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets at FVTOCI, Investments in equity instruments | 32,157 | 1,075 | 39,669
Unsecured subordinate corporate bonds [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets at FVTOCI, Investments in debt instruments | 1,014,872 | 33,931 | 1,016,924
Trade receivables, net | 2,029,690 | 67,860 |
Forward exchange contracts [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial liabilities at FVTPL | 110,990 | 3,711 | 7,597
Call options [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 24,556 | 821 |
Call options [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 24,556 | 821 |
Level 1 of fair value hierarchy [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 4,122,413 | 137,828 | 5,733,055
Level 1 of fair value hierarchy [member] | Quoted ordinary shares [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 3,460,123 | 115,685 | 5,151,255
Level 1 of fair value hierarchy [member] | Open-end mutual funds [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 662,290 | 22,143 | 581,800
Level 2 of fair value hierarchy [Member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 160,869 | 5,378 | 1,690,280
Financial liabilities at FVTPL | 973,571 | 32,550 | 36,655
Level 2 of fair value hierarchy [Member] | Swap contracts [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 56,561 | 1,891 | 1,557,714
Financial liabilities at FVTPL | 862,581 | 28,839 | 29,058
Level 2 of fair value hierarchy [Member] | Forward Exchange Contract [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 104,308 | 3,487 | 32,070
Level 2 of fair value hierarchy [Member] | Private-placement convertible bonds [member] | Hybrid financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL |  |  | 100,496
Level 2 of fair value hierarchy [Member] | Forward exchange contracts [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial liabilities at FVTPL | 110,990 | 3,711 | 7,597
Level 3 of fair value hierarchy [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 1,005,714 | 33,624 | 475,123
Financial assets at FVTOCI | 3,800,465 | 12,706 | 1,597,323
Level 3 of fair value hierarchy [member] | Unquoted preferred shares [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Investments in equity instruments designated at fair value through other comprehensive income | 158,718 | 5,306 |
Level 3 of fair value hierarchy [member] | Unquoted preferred shares [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 377,440 | 12,619 | 275,000
Level 3 of fair value hierarchy [member] | Private-placement funds [member] | Non derivative financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | 603,718 | 20,184 | 200,123
Level 3 of fair value hierarchy [member] | Unquoted ordinary shares [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets at FVTOCI, Investments in equity instruments |  |  | 540,730
Investments in equity instruments designated at fair value through other comprehensive income | 565,028 | 18,891 |
Level 3 of fair value hierarchy [member] | Limited partnership [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets at FVTOCI, Investments in equity instruments | 32,157 | 1,075 | 39,669
Level 3 of fair value hierarchy [member] | Unsecured subordinate corporate bonds [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets at FVTOCI, Investments in debt instruments | 1,014,872 | 33,931 | $ 1,016,924
Trade receivables, net | 2,029,690 | 67,860 |
Level 3 of fair value hierarchy [member] | Call options [member] | Derivative financial instruments [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets mandatorily classified as at FVTPL | $ 24,556 | $ 821 |

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