Derivative Financial Instruments (Narrative) (Details) $ in Millions	Sep. 30, 2026 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Loss on cash flow hedge included in AOCI(L) upon termination	$ 26.5
Loss on cash flow hedge included in AOCI(L) upon termination, after tax	$ 20.1

The amount of the loss on a cash flow hedge that is included in AOCI(L), upon termination of the cash flow hedge, and that will be amortized into earnings over the remaining life of the original cash flow hedge term.

No definition available.

Name:	wash_LossOnCashFlowHedgeIncludedInAOCILUponTermination
Namespace Prefix:	wash_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant