Federal Home Loan Bank Advances (Federal Home Loan Bank Advances Modification Maturity Schedule) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Federal Home Loan Bank, Advances [Line Items]
Federal Home Loan Bank advances	$ 956,786	$ 950,722
Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances [Line Items]
Scheduled maturity in year three	$ 86,222
Weighted average rate for scheduled maturity in year three	2.73%
Scheduled maturity in year four	$ 55,447
Weighted average rate for scheduled maturity in year four	3.65%
Scheduled maturity in year five	$ 9,428
Weighted average rate for scheduled maturity in year five	4.01%
Federal Home Loan Bank advances	$ 956,786	$ 950,700
Total weighted average rate	2.56%
Original Terms of FHLBB Advance Restructuring [Member] \| Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances [Line Items]
Scheduled maturity in year three	$ 20,000
Weighted average rate for scheduled maturity in year three	3.07%
Scheduled maturity in year four	$ 54,634
Weighted average rate for scheduled maturity in year four	3.63%
Scheduled maturity in year five	$ 4,190
Weighted average rate for scheduled maturity in year five	4.27%
Scheduled maturity in year six	$ 0
Weighted average rate for schedule maturity in year six	0.00%
Scheduled maturity in year seven	$ 0
Weighted average rate for schedule maturity in year seven	0.00%
Scheduled maturity in year eight	$ 0
Weighted average rate for schedule maturity in year eight	0.00%
Federal Home Loan Bank advances	$ 78,824
Total weighted average rate	3.52%
Revised Terms of FHLBB Advance Restructuring [Member] \| Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances [Line Items]
Scheduled maturity in year three	$ 0
Weighted average rate for scheduled maturity in year three	0.00%
Scheduled maturity in year four	$ 0
Weighted average rate for scheduled maturity in year four	0.00%
Scheduled maturity in year five	$ 0
Weighted average rate for scheduled maturity in year five	0.00%
Scheduled maturity in year six	$ 40,000
Weighted average rate for schedule maturity in year six	2.45%
Scheduled maturity in year seven	$ 0
Weighted average rate for schedule maturity in year seven	0.00%
Scheduled maturity in year eight	$ 38,824
Weighted average rate for schedule maturity in year eight	3.09%
Federal Home Loan Bank advances	$ 78,824
Total weighted average rate	2.76%

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

The weighted average interest rate applicable to the Federal Home Loan Bank advances which are due from four to five years of the Balance Sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryAverageInterestRateFourToFiveYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average interest rate applicable to the Federal Home Loan Bank advances which are due from three to four years of the Balance Sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(14))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryAverageInterestRateThreeToFourYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average interest rate applicable to the Federal Home Loan Bank advances which are due from two to three years of the Balance Sheet date.

+ References

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryAverageInterestRateTwoToThreeYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

+ Details

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

- Definition

Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

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

- Definition

Federal Home Loan Bank, Advances, Average Interest Rate, Due in Year Eight

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesAverageInterestRateDueinYearEight
Namespace Prefix:	wash_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Federal Home Loan Bank, Advances, Average Interest Rate, Due in Year Seven

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesAverageInterestRateDueinYearSeven
Namespace Prefix:	wash_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Federal Home Loan Bank, Advances, Average Interest Rate, Due in Year Six

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesAverageInterestRateDueinYearSix
Namespace Prefix:	wash_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Federal Home Loan Bank, Advances, Maturities Summary, Average Interest Rate, Total

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesMaturitiesSummaryAverageInterestRateTotal
Namespace Prefix:	wash_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the eighth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesMaturitiesSummaryDueinYearEight
Namespace Prefix:	wash_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the seventh fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesMaturitiesSummaryDueinYearSeven
Namespace Prefix:	wash_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the sixth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	wash_FederalHomeLoanBankAdvancesMaturitiesSummaryDueinYearSix
Namespace Prefix:	wash_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfBostonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wash_FederalHomeLoanBankAdvancesAxis=wash_OriginalTermsofFHLBBAdvanceRestructuringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wash_FederalHomeLoanBankAdvancesAxis=wash_RevisedTermsofFHLBBAdvanceRestructuringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: