Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	$ 5,807	$ 3,135
Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities	7,316	4,298
Interest Rate Swap [Member] \| Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Interest Rate Cash Flow Hedge Asset at Fair Value	0	0
Interest Rate Swap [Member] \| Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Interest Rate Cash Flow Hedge Liability at Fair Value	497	1,012
Interest Rate Lock Commitments [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset not Designated as Hedging Instruments	1,212	392
Interest Rate Lock Commitments [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability not Designated as Hedging Instruments	20	0
Commitments to sell mortgage loans [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset not Designated as Hedging Instruments	13	10
Commitments to sell mortgage loans [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability not Designated as Hedging Instruments	2,028	583
Interest rate swaps with customers [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset not Designated as Hedging Instruments	4,554	2,403
Interest rate swaps with customers [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability not Designated as Hedging Instruments	23	297
Mirror swaps with counterparties [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset not Designated as Hedging Instruments	28	330
Mirror swaps with counterparties [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability not Designated as Hedging Instruments	$ 4,748	$ 2,406

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313

+ Details

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

- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

+ Details

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

- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

+ References

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Definition

Fair value as of the balance sheet date of all interest rate derivative assets designated as cash flow hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

+ Details

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

- Definition

Fair value as of the balance sheet date of all interest rate derivative liabilities designated as cash flow hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

+ Details

Name:	us-gaap_InterestRateCashFlowHedgeLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=wash_InterestRateMirrorSwapsWithCounterpartiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=wash_InterestRateSwapwithcustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: