Note 1 - Nature of Operations (Details Textual)	Dec. 31, 2021
Juanicipio Joint Venture [member]
Statement Line Items [Line Items]
Equity method investment, ownership percentage	44.00%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

No definition available.

Name:	mag_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	mag_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant