Basis of Presentation (Details) (USD $) In Millions	Dec. 31, 2009
Basis of Presentation (Textuals) [Abstract]
Overstatement in each of cash and cash equivalent, accounts payable and accrued expenses and in net cash provided by operating activities	$ 13.1

Name:

gmt_OverstatementInEachOfCashAndCashEquivalentAccountsPayableAndAccruedExpensesAndInNetCashProvidedByOperatingActivities

Namespace Prefix:

gmt

Data Type:

xbrli:monetaryItemType

Balance Type:

debit

Period Type:

instant