XML 100 R59.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Supplemental Cash Flow and Noncash Investing Transactions (Details Textual) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 USD ($) tankContainer | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) tankContainer
Noncash or Part Noncash Divestitures [Line Items] |  |  |
Portfolio proceeds | $ | $ 230.6 | $ 272.8 | $ 269.6
Number of railcars received | tankContainer | 728 |  | 21

X
- Definition Number of railcars received + References No definition available. + Details
Name: | gmt_Numberofrailcarsreceived
Namespace Prefix: | gmt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portfolio proceeds. + References No definition available. + Details
Name: | gmt_PortfolioProceeds
Namespace Prefix: | gmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration