Fair Value Measurements (Narrative) (Details) (Nonrecurring [Member], Level 3 [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Nonrecurring [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowance For Loan Loss Allocation on Collateral Dependent Impaired Loans	$ 2.6	$ 2.0

The allowance for loan loss allocation on collateral dependent impaired loans.

No definition available.

Name:	wash_AllowanceForLoanLossAllocationOnCollateralDependentImpairedLoans
Namespace Prefix:	wash_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant