Derivative Financial Instruments (Policies)	3 Months Ended
Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives Policy	Derivative Financial Instruments The Corporation’s derivative financial instruments are used to manage differences in the amount, timing, and duration of the Corporation’s known or expected cash receipts and its known or expected cash payments principally to manage the Corporation’s interest rate risk. Additionally, the Corporation enters into interest rate derivatives to accommodate the business requirements of its customers. All derivatives are recognized as either assets or liabilities on the balance sheet and are measured at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative and resulting designation. Interest Rate Risk Management Agreements Interest rate swaps are used from time to time as part of the Corporation’s interest rate risk management strategy. Swaps are agreements in which the Corporation and another party agree to exchange interest payments (e.g., fixed-rate for variable-rate payments) computed on a notional principal amount. The credit risk associated with swap transactions is the risk of default by the counterparty. To minimize this risk, the Corporation enters into interest rate agreements only with highly rated counterparties that management believes to be creditworthy. The notional amounts of these agreements do not represent amounts exchanged by the parties and, thus, are not a measure of the potential loss exposure. Cash Flow Hedging Instruments As of March 31, 2015 and December 31, 2014, the Bancorp had two interest rate swap contracts designated as cash flow hedges to hedge the interest rate associated with $22.7 million of variable rate junior subordinated debentures. The effective portion of the changes in fair value of derivatives designated as cash flow hedges is recorded in other comprehensive income and subsequently reclassified to earnings when gains or losses are realized. The ineffective portion of changes in fair value of the derivatives is recognized directly in earnings as interest expense. As of March 31, 2015 and December 31, 2014, the Bancorp has pledged collateral to derivative counterparties in the form of cash totaling $800 thousand and $939 thousand, respectively. The Bancorp may need to post additional collateral in the future in proportion to potential increases in unrealized loss positions. Customer Related Derivative Contracts The Corporation has entered into interest rate swap contracts to help commercial loan borrowers manage their interest rate risk. The interest rate swap contracts with commercial loan borrowers allow them to convert floating-rate loan payments to fixed-rate loan payments. When we enter into an interest rate swap contract with a commercial loan borrower, we simultaneously enter into a “mirror” swap contract with a third party. The third party exchanges the client’s fixed‑rate loan payments for floating-rate loan payments. We retain the risk that is associated with the potential failure of counterparties and the risk inherent in originating loans. As of March 31, 2015 and December 31, 2014, Washington Trust had interest rate swap contracts with commercial loan borrowers with notional amounts of $209.4 million and $165.8 million, respectively, and equal amounts of “mirror” swap contracts with third-party financial institutions. These derivatives are not designated as hedges and therefore, changes in fair value are recognized in earnings. Risk Participation Agreements In 2015, the Corporation entered into a risk participation agreement (“RPA”) with another bank participating in a commercial loan arrangement. The participating bank guarantees the performance on a borrower-related interest rate swap contract. The RPA represents a purchased guarantee that is recorded as an asset and under the RPA the Corporation participates out the risk associated with the interest rate swap position executed with the commercial borrower, for a net fee paid to the participating bank, classified in net gains on interest rate swap contracts. The RPA derivative asset is recorded at fair value and changes in the fair value of the derivative asset are recognized in earnings in the period of change. As of March 31, 2015, the notional amount of the RPA was $12.5 million. Loan Commitments Interest rate lock commitments are extended to borrowers and relate to the origination of residential real estate mortgage loans held for sale. To mitigate the interest rate risk inherent in these rate locks, as well as closed residential real estate mortgage loans held for sale, forward commitments are established to sell individual residential real estate mortgage loans. Both interest rate lock commitments and commitments to sell residential real estate mortgage loans are derivative financial instruments, but do not meet criteria for hedge accounting and, as such are treated as derivatives not designated as hedging instruments. These derivative financial instruments are recorded at fair value and changes in fair value of these commitments are reflected in earnings in the period of change. The Corporation has elected to carry certain closed residential real estate mortgage loans held for sale at fair value, as changes in fair value in these loans held for sale generally offset changes in interest rate lock and forward sale commitments.

Derivative Financial Instruments

The Corporation’s derivative financial instruments are used to manage differences in the amount, timing, and duration of the Corporation’s known or expected cash receipts and its known or expected cash payments principally to manage the Corporation’s interest rate risk. Additionally, the Corporation enters into interest rate derivatives to accommodate the business requirements of its customers. All derivatives are recognized as either assets or liabilities on the balance sheet and are measured at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative and resulting designation.

Interest Rate Risk Management Agreements

Interest rate swaps are used from time to time as part of the Corporation’s interest rate risk management strategy. Swaps are agreements in which the Corporation and another party agree to exchange interest payments (e.g., fixed-rate for variable-rate payments) computed on a notional principal amount. The credit risk associated with swap transactions is the risk of default by the counterparty. To minimize this risk, the Corporation enters into interest rate agreements only with highly rated counterparties that management believes to be creditworthy. The notional amounts of these agreements do not represent amounts exchanged by the parties and, thus, are not a measure of the potential loss exposure.

Cash Flow Hedging Instruments

As of March 31, 2015 and December 31, 2014, the Bancorp had two interest rate swap contracts designated as cash flow hedges to hedge the interest rate associated with $22.7 million of variable rate junior subordinated debentures. The effective portion of the changes in fair value of derivatives designated as cash flow hedges is recorded in other comprehensive income and subsequently reclassified to earnings when gains or losses are realized. The ineffective portion of changes in fair value of the derivatives is recognized directly in earnings as interest expense. As of March 31, 2015 and December 31, 2014, the Bancorp has pledged collateral to derivative counterparties in the form of cash totaling $800 thousand and $939 thousand, respectively. The Bancorp may need to post additional collateral in the future in proportion to potential increases in unrealized loss positions.

Customer Related Derivative Contracts

The Corporation has entered into interest rate swap contracts to help commercial loan borrowers manage their interest rate risk. The interest rate swap contracts with commercial loan borrowers allow them to convert floating-rate loan payments to fixed-rate loan payments. When we enter into an interest rate swap contract with a commercial loan borrower, we simultaneously enter into a “mirror” swap contract with a third party. The third party exchanges the client’s fixed‑rate loan payments for floating-rate loan payments. We retain the risk that is associated with the potential failure of counterparties and the risk inherent in originating loans. As of March 31, 2015 and December 31, 2014, Washington Trust had interest rate swap contracts with commercial loan borrowers with notional amounts of $209.4 million and $165.8 million, respectively, and equal amounts of “mirror” swap contracts with third-party financial institutions. These derivatives are not designated as hedges and therefore, changes in fair value are recognized in earnings.

Risk Participation Agreements

In 2015, the Corporation entered into a risk participation agreement (“RPA”) with another bank participating in a commercial loan arrangement. The participating bank guarantees the performance on a borrower-related interest rate swap contract. The RPA represents a purchased guarantee that is recorded as an asset and under the RPA the Corporation participates out the risk associated with the interest rate swap position executed with the commercial borrower, for a net fee paid to the participating bank, classified in net gains on interest rate swap contracts. The RPA derivative asset is recorded at fair value and changes in the fair value of the derivative asset are recognized in earnings in the period of change. As of March 31, 2015, the notional amount of the RPA was $12.5 million.

Loan Commitments

Interest rate lock commitments are extended to borrowers and relate to the origination of residential real estate mortgage loans held for sale. To mitigate the interest rate risk inherent in these rate locks, as well as closed residential real estate mortgage loans held for sale, forward commitments are established to sell individual residential real estate mortgage loans. Both interest rate lock commitments and commitments to sell residential real estate mortgage loans are derivative financial instruments, but do not meet criteria for hedge accounting and, as such are treated as derivatives not designated as hedging instruments. These derivative financial instruments are recorded at fair value and changes in fair value of these commitments are reflected in earnings in the period of change. The Corporation has elected to carry certain closed residential real estate mortgage loans held for sale at fair value, as changes in fair value in these loans held for sale generally offset changes in interest rate lock and forward sale commitments.