Significant accounting policies - Leases (Details)	12 Months Ended
Dec. 31, 2021
Maximum
Disclosure of Finance Leases [Line Items]
Lease term	22 years

[Line Items] for Disclosure of Finance Leases [Table]

No definition available.

Name:	mx_DisclosureofFinanceLeasesLineItems
Namespace Prefix:	mx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration