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Income Taxes (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Current tax expense:      
Federal $ 22,046,000us-gaap_CurrentFederalTaxExpenseBenefit $ 22,612,000us-gaap_CurrentFederalTaxExpenseBenefit $ 19,122,000us-gaap_CurrentFederalTaxExpenseBenefit
State 2,386,000us-gaap_CurrentStateAndLocalTaxExpenseBenefit 2,531,000us-gaap_CurrentStateAndLocalTaxExpenseBenefit 1,879,000us-gaap_CurrentStateAndLocalTaxExpenseBenefit
Total current tax expense 24,432,000us-gaap_CurrentIncomeTaxExpenseBenefit 25,143,000us-gaap_CurrentIncomeTaxExpenseBenefit 21,001,000us-gaap_CurrentIncomeTaxExpenseBenefit
Deferred tax expense (benefit) 2,964,000us-gaap_DeferredIncomeTaxExpenseBenefit (1,426,000)us-gaap_DeferredIncomeTaxExpenseBenefit 1,440,000us-gaap_DeferredIncomeTaxExpenseBenefit
Total income tax expense 27,396,000us-gaap_IncomeTaxExpenseBenefit 23,717,000us-gaap_IncomeTaxExpenseBenefit 22,441,000us-gaap_IncomeTaxExpenseBenefit
Components of deferred tax assets and liabilities [Abstract]      
Benefits and deferred remuneration (3,885,000)us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits (4,256,000)us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits  
Difference in reporting the allowance for loan losses, net 21,006,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses 22,774,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses  
Other income or expense not yet reported for tax purposes 2,325,000trst_OtherIncomeOrExpenseNotYetReportedForTaxPurposes 3,008,000trst_OtherIncomeOrExpenseNotYetReportedForTaxPurposes  
Depreciable assets (1,040,000)us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment (1,309,000)us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment  
Other items 0us-gaap_DeferredTaxAssetsTaxDeferredExpenseOther 1,153,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseOther  
Net deferred tax assets at end of year 18,406,000us-gaap_DeferredTaxAssetsLiabilitiesNet 21,370,000us-gaap_DeferredTaxAssetsLiabilitiesNet 19,944,000us-gaap_DeferredTaxAssetsLiabilitiesNet
Net deferred tax assets at beginning of year 21,370,000us-gaap_DeferredTaxAssetsLiabilitiesNet 19,944,000us-gaap_DeferredTaxAssetsLiabilitiesNet  
Deferred tax expense (benefit) 2,964,000us-gaap_DeferredIncomeTaxExpenseBenefit (1,426,000)us-gaap_DeferredIncomeTaxExpenseBenefit 1,440,000us-gaap_DeferredIncomeTaxExpenseBenefit
Deferred tax assets, unrealized losses on available-for-sale securities 2,400,000us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross 12,000,000us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross  
Deferred tax assets, unrecognized overfunded position in company's pension and postretirement benefit plans 535,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits 0us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits  
Deferred tax liability, unrecognized overfunded position in company's pension and postretirement benefit plans   2,800,000trst_DeferredTaxLiabilityTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits  
Reconciliation from statutory federal income tax rate to effective tax rate [Abstract]      
Statutory federal income tax rate (in hundredths) 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Increase/(decrease) in taxes resulting from: [Abstract]      
Tax exempt income (in hundredths) (0.10%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome (0.30%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome (0.70%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome
State income tax (including alternative minimum tax),net of federal tax benefit 2.70%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 2.30%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 2.30%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Other items (in hundredths) 0.70%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 0.30%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 0.80%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Effective income tax rate (in hundredths) 38.30%us-gaap_EffectiveIncomeTaxRateContinuingOperations 37.30%us-gaap_EffectiveIncomeTaxRateContinuingOperations 37.40%us-gaap_EffectiveIncomeTaxRateContinuingOperations
Unrecognized pre-tax benefit and changes in those benefits [Roll Forward]      
Unrecognized tax benefit, beginning balance 213,000us-gaap_UnrecognizedTaxBenefits 213,000us-gaap_UnrecognizedTaxBenefits  
Change in unrecognized tax reserve 0us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions 0us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions  
Unrecognized tax benefit, ending balance $ 213,000us-gaap_UnrecognizedTaxBenefits $ 213,000us-gaap_UnrecognizedTaxBenefits $ 213,000us-gaap_UnrecognizedTaxBenefits
Federal [Member] | Minimum [Member]      
Open Tax Years [Abstract]      
Open tax year 2011    
Federal [Member] | Maximum [Member]      
Open Tax Years [Abstract]      
Open tax year 2014    
New York State [Member] | Minimum [Member]      
Open Tax Years [Abstract]      
Open tax year 2011    
New York State [Member] | Maximum [Member]      
Open Tax Years [Abstract]      
Open tax year 2014