Loans (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Loans Receivable Net Deferred Cost Originated	$ 4,500	$ 3,800
Loans Receivable Net Deferred Premium on Purchased Loans	794	878
Loans Pledged as Collateral	1,800,000	1,600,000
Past due loans included in nonaccrual loans	8,600	11,800
Mortgage Loans in Process of Foreclosure	$ 2,200	$ 4,400

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL49126937-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects cumulative amount of net costs paid by borrowers which have not been taken into expense.

+ References

No definition available.

+ Details

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

- Definition

Reflects premiums over or discounts from face amounts of acquired loans that are being amortized into income as an adjustment to yield.

+ References

No definition available.

+ Details

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

- Definition

Reflects carrying value of loans which are past due and on nonaccrual status.

+ References

No definition available.

+ Details

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