Income Taxes (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Provision for Income Taxes, Equity Method Investment	$ 18.3	$ 16.5	$ 2.0
Equity Method Investment, Summarized Financial Information, Income Tax		15.2	9.2
Income before income taxes
Domestic	137.9	66.0	80.5
Foreign	93.3	93.0	63.3
Income before Income Taxes and Share of Affiliates’ Earnings	$ 231.2gmt_IncomeBeforeIncomeTaxes	$ 159.0gmt_IncomeBeforeIncomeTaxes	$ 143.8gmt_IncomeBeforeIncomeTaxes

Equity Method Investment, Summarized Financial Information, Income Tax

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- Definition

Income before income taxes.

+ References

No definition available.

+ Details

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- Definition

Provision for Income Taxes, Equity Method Investment

+ References

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- Definition

The portion of earnings or loss from continuing operations before income taxes that is attributable to domestic operations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h)(1)(i))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

The portion of earnings or loss from continuing operations before income taxes that is attributable to foreign operations, which is defined as Income or Loss generated from operations located outside the entity's country of domicile.

+ References

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