Regulatory and Legal Developments - Additional Information (Detail) (USD $)	9 Months Ended
Sep. 30, 2013 Plaintiff
Legal Proceedings And Contingencies [Line Items]
Damage incurred due to the extra-contractual claims against STGC and STGM based on application of Mexican law	$ 0
Number Of Plaintiffs	8

Amount of damages paid to the plaintiff in the legal matter.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

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-Section 50

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

-Publisher FASB

-Name Accounting Standards Codification

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

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-Name Accounting Standards Codification

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