Name:	mag_DiscontinuedOperationsLineItems
Namespace Prefix:	mag_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of gain (loss), after tax expense or benefit and not previously recognized, resulting from the sale of a business component.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

+ Details

Name:	us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.12)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 13

-Article 7

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 05

-Paragraph 15

-Article 3

+ Details

Name:	us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

+ Details

Name:	us-gaap_GainLossRelatedToLitigationSettlement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 19

-URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683

+ Details

Name:	us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								6 Months Ended		12 Months Ended
	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 30, 2012	Sep. 30, 2012	Jul. 01, 2012	Apr. 01, 2012	Jan. 01, 2012	Jan. 02, 2011	Dec. 29, 2013	Dec. 30, 2012	Jan. 01, 2012	Jul. 03, 2011
Discontinued Operations [Line Items]
Income (loss) from discontinued operations before interest and income taxes									$ (39)		$ (627)	$ 703		$ (1,154)
Income on sale of telecom power systems business									0		0	32		0
Gain from settlement agreement, net of fees									0		0	4,962		0
Income (loss) from discontinued operations, net of tax	(365)	(161)	(28)	(73)	204	(159)	946	4,706	(39)	(533)	(627)	5,697	(660)	(1,154)
Legal Settlement [Member]
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax												5,000
Non-Cash Adjustments for Liabilities [Member]
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax												1,200
Legal Fees and Other [Member]
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax									700		(200)	(500)		(300)
Adjustments to Insurance Reserves [Member]
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax									(300)
Environmental Charges [Member]
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax									(200)		(300)			(500)
Legal Fees Related to Abestos Issues [Member]
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax									$ (200)					$ (300)