Share-based Payment Arrangements - Summary of Inputs Related to Fair Value of Share Options (Detail) - 12 months ended Dec. 31, 2017	TWD ($) yr	CNY (¥) yr
ASE Inc. option plans [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share price at the grant date \| $	$ 36.5
Exercise prices \| $	$ 36.5
Expected volatility	27.02%	27.02%
Expected lives \| yr	10	10
Expected dividend yield	4.00%	4.00%
Risk free interest rates	1.34%	1.34%
USISH option plans [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share price at the grant date \| ¥		¥ 15.2
Exercise prices \| ¥		¥ 15.5
Expected lives \| yr	10	10
Expected dividend yield	0.87%	0.87%
USISH option plans [member] \| Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Expected volatility	40.33%	40.33%
Risk free interest rates	3.06%	3.06%
USISH option plans [member] \| Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Expected volatility	45.00%	45.00%
Risk free interest rates	3.13%	3.13%

The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The option life of share options granted.

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The implied yield currently available on zero-coupon government issues of the country in whose currency the exercise price for share options granted is expressed, with a remaining term equal to the expected term of the option being valued (based on the option's remaining contractual life and taking into account the effects of expected early exercise). [Refer: Government [member]]

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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The exercise price of share options granted.

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The percentage of an expected dividend used to calculate the fair value of share options granted.

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The weighted average share price used as input to the option pricing model to calculate the fair value of share options granted. [Refer: Option pricing model [member]; Weighted average [member]]

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