Leases (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013 Corporations	Dec. 31, 2012	Dec. 31, 2011
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense		$ 134.0	$ 133.3	$ 137.3
gmt_CapitalLeasePurchaseCommitmentsAmount	119.0
gmt_CapitalLeasePurchaseCommitmentsNumber	3,275
gmt_OperatingLeasePurchaseCommitmentsNumber	1,308
Leases (Textual) [Abstract]
Income from leveraged leases, net of taxes		0	0.2	4.6
Rental income from usage rents		21.3	18.2	13.7
Deferred initial direct costs of direct financial leases		0.4	0.8
Number of corporations		2
Recourse Operating Leases [Member]
Operating Leased Assets [Line Items]
gmt_OperatingLeasePurchaseCommitmentsAmount	$ 32.2