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v2.4.1.9

Debt (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013
Commercial Paper and Borrowings Under Bank Credit Facilities |  |
Balance | $ 72.1 us-gaap_OtherShortTermBorrowings | $ 23.6 us-gaap_OtherShortTermBorrowings
Weighted average interest rate | 0.56%us-gaap_ShortTermDebtWeightedAverageInterestRate | 0.80%us-gaap_ShortTermDebtWeightedAverageInterestRate
Outstanding balances of debt obligations and the applicable interest rates |  |
Total debt principal | 4,203.8 us-gaap_LongTermDebt | 3,842.0 us-gaap_LongTermDebt
Debt discount, net | (8.6)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet | (8.9)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
Debt adjustment for fair value hedges | 0.6 gmt_DebtAdjustmentForFairValueHedges | 5.4 gmt_DebtAdjustmentForFairValueHedges
Total Debt | 4,195.8 us-gaap_DebtInstrumentCarryingAmount | 3,838.5 us-gaap_DebtInstrumentCarryingAmount
Recourse Fixed Rate Debt Unsecured One [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Apr. 14, 2005 |
Final Maturity | Apr. 15, 2015 |
Fixed Interest Rate | 5.70%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredOneMember |
Total Debt | 100.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredOneMember | 100.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredOneMember
Recourse Fixed Rate Debt Unsecured Two [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Feb. 05, 2010 |
Final Maturity | May 15, 2015 |
Fixed Interest Rate | 4.75%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwoMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwoMember | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwoMember
Recourse Fixed Rate Debt Unsecured Three [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 22, 2005 |
Final Maturity | Dec. 22, 2015 |
Fixed Interest Rate | 5.75%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredThreeMember |
Total Debt | 70.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredThreeMember | 85.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredThreeMember
Recourse Fixed Rate Debt Unsecured Four [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 03, 2006 |
Final Maturity | Mar. 01, 2016 |
Fixed Interest Rate | 5.80%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFourMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFourMember | 200.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFourMember
Recourse Fixed Rate Debt Unsecured Five [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Nov. 19, 2010 |
Final Maturity | Jul. 15, 2016 |
Fixed Interest Rate | 3.50%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFiveMember |
Total Debt | 200.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFiveMember | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFiveMember
Recourse Fixed Rate Debt Unsecured Six [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Sep. 20, 2011 |
Final Maturity | Jul. 15, 2016 |
Fixed Interest Rate | 3.50%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSixMember |
Total Debt | 100.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSixMember | 100.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSixMember
Recourse Fixed Rate Debt Unsecured Seven [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 04, 2014 |
Final Maturity | Mar. 04, 2017 |
Fixed Interest Rate | 1.25%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSevenMember |
Total Debt | 300.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSevenMember | 0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSevenMember
Recourse Fixed Rate Debt Unsecured Eight [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Feb. 06, 2008 |
Final Maturity | Feb. 15, 2018 |
Fixed Interest Rate | 6.00%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredEightMember |
Total Debt | 200.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredEightMember | 200.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredEightMember
Recourse Fixed Rate Debt Unsecured Nine [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 19, 2013 |
Final Maturity | Jul. 30, 2018 |
Fixed Interest Rate | 2.38%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredNineMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredNineMember | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredNineMember
Recourse Fixed Rate Debt Unsecured Ten [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 27, 2010 |
Final Maturity | Oct. 31, 2018 |
Fixed Interest Rate | 3.84%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTenMember |
Total Debt | 15.7 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTenMember | 22.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTenMember
Recourse Fixed Rate Debt Unsecured Eleven [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Nov. 29, 2010 |
Final Maturity | Nov. 30, 2018 |
Fixed Interest Rate | 3.70%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredElevenMember |
Total Debt | 12.1 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredElevenMember | 17.2 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredElevenMember
Recourse Fixed Rate Debt Unsecured Twelve [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Nov. 19, 2013 |
Final Maturity | Mar. 15, 2019 |
Fixed Interest Rate | 2.50%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwelveMember |
Total Debt | 300.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwelveMember | 300.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwelveMember
Recourse Fixed Rate Debt Unsecured Thirteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 04, 2014 |
Final Maturity | Jul. 30, 2019 |
Fixed Interest Rate | 2.50%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredThirteenMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredThirteenMember | 0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredThirteenMember
Recourse Fixed Rate Debt Unsecured Fourteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Oct. 31, 2014 |
Final Maturity | Mar. 30, 2020 |
Fixed Interest Rate | 2.60%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFourteenMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFourteenMember | 0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFourteenMember
Recourse Fixed Rate Debt Unsecured Fifteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | May 27, 2011 |
Final Maturity | Jun. 01, 2021 |
Fixed Interest Rate | 4.85%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFifteenMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFifteenMember | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredFifteenMember
Recourse Fixed Rate Debt Unsecured Sixteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Sep. 20, 2011 |
Final Maturity | Jun. 01, 2021 |
Fixed Interest Rate | 4.85%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSixteenMember |
Total Debt | 50.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSixteenMember | 50.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSixteenMember
Recourse Fixed Rate Debt Unsecured Seventeen [Member] [Domain] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Jun. 11, 2012 |
Final Maturity | Jun. 15, 2022 |
Fixed Interest Rate | 4.75%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSeventeenMemberDomain |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSeventeenMemberDomain | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredSeventeenMemberDomain
Recourse Fixed Rate Debt Unsecured Eighteen [Member] [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 19, 2013 |
Final Maturity | Mar. 30, 2023 |
Fixed Interest Rate | 3.90%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredEighteenMemberMember |
Total Debt | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredEighteenMemberMember | 250.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredEighteenMemberMember
Recourse Fixed Rate Debt Unsecured Nineteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 04, 2014 |
Final Maturity | Mar. 15, 2044 |
Fixed Interest Rate | 5.20%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredNineteenMember |
Total Debt | 300.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredNineteenMember | 0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredNineteenMember
Recourse Fixed Rate Debt Unsecured Twenty [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Apr. 30, 2009 |
Final Maturity | May 15, 2014 |
Fixed Interest Rate | 8.75%us-gaap_LongTermDebtPercentageBearingFixedInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwentyMember |
Total Debt | 0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwentyMember | 300.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtUnsecuredTwentyMember
Recourse Fixed Rate Debt [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Total Debt | 3,647.8 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtMember | 2,874.2 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFixedRateDebtMember
Recourse Floating Rate Debt Unsecured One [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 15, 2010 |
Final Maturity | Oct. 31, 2015 |
Floating Interest Rate | 1.47%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredOneMember |
Total Debt | 24.8 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredOneMember | 36.4 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredOneMember
Recourse Floating Rate Debt Unsecured Three [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Sep. 02, 2011 |
Final Maturity | Aug. 31, 2016 |
Floating Interest Rate | 1.13%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredThreeMember |
Total Debt | 8.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredThreeMember | 11.5 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredThreeMember
Recourse Floating Rate Debt Unsecured Four [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 29, 2006 |
Final Maturity | Sep. 30, 2016 |
Floating Interest Rate | 2.08%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFourMember |
Total Debt | 18.9 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFourMember | 32.2 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFourMember
Recourse Floating Rate Debt Secured One [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 19, 2011 |
Final Maturity | Dec. 19, 2020 |
Floating Interest Rate | 2.10%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtSecuredOneMember |
Total debt principal | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtSecuredOneMember | 91.1 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtSecuredOneMember
Recourse Floating Rate Debt Unsecured Five [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Jun. 29, 2007 |
Final Maturity | Sep. 30, 2016 |
Floating Interest Rate | 2.03%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFiveMember |
Total Debt | 8.5 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFiveMember | 14.4 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFiveMember
Recourse Floating Rate Debt Unsecured Six [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 18, 2007 |
Final Maturity | Oct. 31, 2016 |
Floating Interest Rate | 1.98%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSixMember |
Total Debt | 12.7 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSixMember | 21.6 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSixMember
Recourse Floating Rate Debt Unsecured Seven [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 21, 2012 |
Final Maturity | Dec. 21, 2017 |
Floating Interest Rate | 1.39%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSevenMember |
Total Debt | 100.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSevenMember | 100.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSevenMember
Recourse Floating Rate Debt Unsecured Eight [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Jan. 22, 2013 |
Final Maturity | Dec. 21, 2017 |
Floating Interest Rate | 1.39%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredEightMember |
Total Debt | 10.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredEightMember | 70.0 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredEightMember
Recourse Floating Rate Debt Secured Two [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 06, 2011 |
Final Maturity | Aug. 31, 2016 |
Floating Interest Rate | 1.57%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtSecuredTwoMember |
Total Debt | 15.3 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtSecuredTwoMember | 22.1 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtSecuredTwoMember
Recourse Floating Rate Debt Unsecured Nine [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Aug. 31, 2012 |
Final Maturity | Dec. 31, 2019 |
Floating Interest Rate | 2.33%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredNineMember |
Total Debt | 60.5 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredNineMember | 68.7 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredNineMember
Recourse Floating Rate Debt Unsecured Ten [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Jun. 27, 2013 |
Final Maturity | Dec. 31, 2020 |
Floating Interest Rate | 1.87%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredTenMember |
Total debt principal | 121.0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredTenMember | 137.5 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredTenMember
Recourse Floating Rate Debt Un Secured Eleven [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Oct. 30, 2013 |
Final Maturity | Dec. 31, 2020 |
Floating Interest Rate | 1.91%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredElevenMember |
Total debt principal | 30.2 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredElevenMember | 34.4 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredElevenMember
Recourse Floating Rate Debt Un Secured Twelve [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | May 05, 2014 |
Final Maturity | Dec. 31, 2020 |
Floating Interest Rate | 1.99%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredTwelveMember |
Total debt principal | 30.2 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredTwelveMember | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredTwelveMember
Recourse Floating Rate Debt Un Secured Thirteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Aug. 28, 2014 |
Final Maturity | Aug. 28, 2024 |
Floating Interest Rate | 1.54%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredThirteenMember |
Total debt principal | 100.0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredThirteenMember | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnSecuredThirteenMember
Recourse Floating Rate Debt Unsecured Fourteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Mar. 01, 2010 |
Final Maturity | Feb. 28, 2015 |
Floating Interest Rate | 1.83%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFourteenMember |
Total debt principal | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFourteenMember | 13.7 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFourteenMember
Recourse Floating Rate Debt Unsecured Fifteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Dec. 12, 2011 |
Final Maturity | Jun. 12, 2017 |
Floating Interest Rate | 1.63%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFifteenMember |
Total debt principal | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFifteenMember | 103.5 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredFifteenMember
Recourse Floating Rate Debt Unsecured Sixteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Aug. 12, 2013 |
Final Maturity | Jun. 12, 2017 |
Floating Interest Rate | 1.63%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSixteenMember |
Total debt principal | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSixteenMember | 71.1 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSixteenMember
Recourse Floating Rate Debt Unsecured Seventeen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Jan. 12, 2012 |
Final Maturity | Jun. 12, 2017 |
Floating Interest Rate | 1.63%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSeventeenMember |
Total debt principal | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSeventeenMember | 31.5 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredSeventeenMember
Recourse Floating Rate Debt Unsecured Eighteen [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Feb. 21, 2013 |
Final Maturity | Dec. 21, 2017 |
Floating Interest Rate | 1.81%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredEighteenMember |
Total debt principal | 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredEighteenMember | 35.0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtUnsecuredEighteenMember
Total Recourse Floating Rate Debt [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Total debt principal | 540.1 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtMember | 894.7 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_RecourseFloatingRateDebtMember
Nonrecourse Fixed Rate Debt Secured One [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Date of Issue | Sep. 30, 1997 |
Final Maturity | Sep. 20, 2016 |
Floating Interest Rate | 6.69%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFixedRateDebtSecuredOneMember |
Total debt principal | 15.9 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFixedRateDebtSecuredOneMember | 25.4 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFixedRateDebtSecuredOneMember
Total Nonrecourse Fixed Rate Debt [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Total debt principal | 15.9 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFixedRateDebtMember | 25.4 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFixedRateDebtMember
Nonrecourse Floating Rate Debt Secured One [Member] |  |
Outstanding balances of debt obligations and the applicable interest rates |  |
Final Maturity | May 08, 2014 |
Floating Interest Rate | 1.40%us-gaap_LongTermDebtPercentageBearingVariableInterestRate / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFloatingRateDebtSecuredOneMember |
Total debt principal | $ 0 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFloatingRateDebtSecuredOneMember | $ 47.7 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = gmt_NonrecourseFloatingRateDebtSecuredOneMember

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