Loans (Narrative - Credit Quality Indicators) (Details) - rating	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Weighted Average Risk Rating, Commercial Loans	4.70	4.68

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