Leases - Additional Information (Detail)	3 Months Ended
Mar. 31, 2019
Maximum [Member]
Lease Agreements Remaining Term of Lease	15 years
Lessee Lease Option To Extend	10 years
Minimum [Member]
Lease Agreements Remaining Term of Lease	1 year
Lessee Lease Option To Extend	1 year

Lease agreements remaining lease term for finance and operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

No definition available.

Name:	mx_WeightedAverageRemainingLeaseTerm
Namespace Prefix:	mx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration