Loans (Narrative - Credit Quality Indicators) (Details) - rating	Sep. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Weighted Average Commercial Loan Portfolio Risk Rating	4.74	4.70

The represents the weighted average risk rating for commercial loans.

No definition available.

Name:	wash_WeightedAverageRiskRatingCommercialLoans
Namespace Prefix:	wash_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant