Note 6 - Investments in Associate ("Minera Juanicipio S.A. DE C.V.") - Investment Relating to Interests in Juancipio Property and Minera Juancipio (Details) (Parentheticals)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Statement Line Items [Line Items]
Joint Venture Expenditures Incurred Percentage	100.00%	100.00%

The percentage of joint venture costs incurred by MAG Silver Corp.

No definition available.

Name:	mag_JointVentureFinancialInformationSummaryIncludingAdjustmentsMadeByMagSilverCorp
Namespace Prefix:	mag_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration