Loans Loans (Troubled Debt Restructurings Subsequent Default) (Details) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($) loan	Jun. 30, 2016 USD ($) loan	Jun. 30, 2017 USD ($) loan	Jun. 30, 2016 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of loans modified as a troubled debt restructuring	0	2	0	2
Payment Default [Member]
Financing Receivable, Modifications [Line Items]
Number of loans modified as a troubled debt restructuring	3	4	4	4
Recorded investment on TDR modifications with payment default \| $	$ 1,100	$ 577	$ 1,900	$ 577

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=wash_PaymentDefaultMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: