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Summary of Significant Accounting Policies (Details)
12 Months Ended
Dec. 31, 2014
Accounting Policies [Line Items]  
Federal Home Loan Bank Stock, redemption period, years after membership termination 5 years
Number of days overdue to be classified as nonaccrual 90 days
Troubled debt restructured loans, management determination of loans on nonaccrual status to return to accrual status, period 6 months
Time loan is reported as TDR from date of restructuring 1 year
Equity Method Investment, Number of Investments 2wash_EquityMethodInvestmentNumberOfInvestments
Number of low-income housing complexes included in equity method investments 2wash_EquityMethodInvestmentsNumberOfLowIncomeHousingComplexes
Equity Method Investee, One [Member]  
Accounting Policies [Line Items]  
Equity method investment, ownership percentage 99.90%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wash_EquityMethodInvesteeOneMember
Equity Method Investee, Two [Member]  
Accounting Policies [Line Items]  
Equity method investment, ownership percentage 99.90%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wash_EquityMethodInvesteeTwoMember
Premises and Improvements [Member] | Minimum [Member]  
Accounting Policies [Line Items]  
Estimated useful life (in years) 5 years
Premises and Improvements [Member] | Maximum [Member]  
Accounting Policies [Line Items]  
Estimated useful life (in years) 40 years
Furniture, Fixtures and Equipment [Member] | Minimum [Member]  
Accounting Policies [Line Items]  
Estimated useful life (in years) 3 years
Furniture, Fixtures and Equipment [Member] | Maximum [Member]  
Accounting Policies [Line Items]  
Estimated useful life (in years) 20 years