Defined Benefit Pension Plans (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Defined Benefit Pension Plan Amendment, Pension Liability Reduction	$ 17.5
Defined Benefit Pension Plan Amendment, Accumulated Other Comprehensive Income Increase	$ 11.2

This amount represents the defined benefit pension plan amendment accumulated other comprehensive income increase.

No definition available.

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