Investments in Affiliated Companies Investments in Affililated Companies (Details) In Millions, unless otherwise specified	9 Months Ended		3 Months Ended			9 Months Ended
	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Jun. 30, 2013 Singco/Somagas [Member] USD ($)	Sep. 30, 2013 Aae Cargo Ag [Member] USD ($)	Sep. 30, 2013 Aae Cargo Ag [Member] EUR (€)	Sep. 30, 2013 Aae Cargo Ag [Member] USD ($)
Investments in and Advances to Affiliates [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent				37.50%	37.50%	37.50%
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax				$ 9.3
gmt_SalePrice				114.1	84.5
Proceeds from Divestiture of Businesses and Interests in Affiliates			23.0		17.0
Portfolio Proceeds	$ 286.6	$ 260.2				$ 91.1	[1]

[1] (b)In 2013, proceeds from the sale of our 37.5% interest in AAE included receipt of a note in the amount of $91.1 million.