XML 56 R41.htm IDEA: XBRL DOCUMENT
v3.19.1

Fair Value Disclosure Fair Value Disclosure - Other Financial Instruments (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Reported Value Measurement [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Recourse fixed rate debt | $ 4,436.1 | $ 3,933.4
Recourse floating rate debt | 361.4 | 522.7
Estimate of Fair Value Measurement [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Recourse fixed rate debt | 4,470.6 | 3,836.0
Recourse floating rate debt | $ 359.8 | $ 515.1

X
- Definition Recourse fixed rate debt fair value disclosure. + References No definition available. + Details
Name: | gmt_RecourseFixedRateDebtFairValueDisclosure
Namespace Prefix: | gmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Recourse floating rate debt fair value disclosure. + References No definition available. + Details
Name: | gmt_RecourseFloatingRateDebtFairValueDisclosure
Namespace Prefix: | gmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |