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Capital Stock - Additional Information (Detail)	0 Months Ended	12 Months Ended
	Nov. 10, 2014	Dec. 31, 2014 Vote
Equity [Abstract]
Preference shares included in authorized capital stock		99,760,000us-gaap_PreferredStockSharesAuthorized
Shares issued or outstanding		0us-gaap_PreferredStockSharesIssued
Number of votes per share		1mga_NumberOfVotesPerShare
Number of common stock shares to be purchased under the Bid	20,000,000mga_NumberOfCommonStockSharesToBeRepurchased
Percentage of issued and outstanding common shares	9.70%mga_PercentageOfCommonStockSharesIssuedAndOutstanding
Commencement date of Bid		November 13, 2014
Termination date of Bid		November 12, 2015

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- Definition

Commencement date of bid.

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- Definition

Number of common stock shares to be repurchased.

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- Definition

Number of votes per share.

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- Definition

Percentage of common stock shares issued and outstanding.

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- Definition

Termination date of bid.

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- Details

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- Definition

The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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- Definition

Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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