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Allowance for Loan Losses (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]        
Allowance for loan losses $ 28,023us-gaap_LoansAndLeasesReceivableAllowance $ 27,886us-gaap_LoansAndLeasesReceivableAllowance $ 30,873us-gaap_LoansAndLeasesReceivableAllowance $ 29,802us-gaap_LoansAndLeasesReceivableAllowance
Reclassification of unallocated allowance [Member]        
Financing Receivable, Allowance for Credit Losses [Line Items]        
Allowance for loan losses   $ 5,200us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wash_ReclassificationofunallocatedallowanceMember		 $ 5,500us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= wash_ReclassificationofunallocatedallowanceMember