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Share-based Payment Arrangements - Summary of ASE Inc. Option Plans Outstanding Share Options (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
ASE Inc. option plans [member] | Fourth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted Average Remaining Contractual Life (Years)	6 months	1 year 6 months
ASE Inc. option plans [member] | Fifth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	$ 73.0	$ 73.0
Weighted Average Remaining Contractual Life (Years)	5 years 8 months 12 days	6 years 8 months 12 days
ASE Inc. option plans [member] | Bottom of range [member] | Fourth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	$ 40.8	$ 40.8
ASE Inc. option plans [member] | Top of range [member] | Fourth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	45.2	45.2
The Company Option Plans [member] | First share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	$ 54.4	$ 56.4
Weighted Average Remaining Contractual Life (Years)	8 years 10 months 24 days	9 years 10 months 24 days

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+ References

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The exercise price of outstanding share options.

+ References

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The weighted average remaining contractual life of outstanding share options. [Refer: Weighted average [member]]

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