Related Party Transactions - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018 TWD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 TWD ($)
Disclosure of transactions between related parties [Line Items]
Acquisition of investment in associate	$ 794,694		$ 1,373,486
ChipMOS BVI and Unimos Shanghai [member]
Disclosure of transactions between related parties [Line Items]
Acquisition of investment in associate	$ 794,694	$ 25,962	$ 1,373,486

The cash outflow for the purchase of interests in associates. [Refer: Associates [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2019-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2019-en-r&anchor=para_16&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_PurchaseOfInterestsInAssociates
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration