Derivative Financial Instruments (Policies)	9 Months Ended
Sep. 30, 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 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. During the third quarter of 2015, one of the interest rate swap contracts matured. As a result, as of September 30, 2015, the Bancorp had one interest rate swap contract designated as a cash flow hedge to hedge the interest rate associated with $14.4 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 September 30, 2015 and December 31, 2014, the Bancorp has pledged collateral to derivative counterparties in the form of cash totaling $550 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 September 30, 2015 and December 31, 2014, Washington Trust had interest rate swap contracts with commercial loan borrowers with notional amounts of $272.6 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 During 2015, the Corporation entered into risk participation agreements (“RPAs”) with other banks participating in commercial loan arrangements. Participating banks guarantee the performance on borrower-related interest rate swap contracts. RPAs are derivative financial instruments and are recorded at fair value. Changes in the fair value of the derivative assets and liabilities are recognized in earnings in the period of change. Under a risk participation-out agreement, a derivative asset, the Corporation participates out a portion of the credit risk associated with the interest rate swap position executed with the commercial borrower, for a fee paid to the participating bank. Under a risk participation-in agreement, a derivative liability, the Corporation assumes, or participates in, a portion of the credit risk associated with the interest rate swap position with the commercial borrower, for a fee received from the other bank. As of September 30, 2015, the notional amounts of the risk participation-out agreements and risk participation-in agreements were $25.3 million and $8.0 million, respectively. 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 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. During the third quarter of 2015, one of the interest rate swap contracts matured. As a result, as of September 30, 2015, the Bancorp had one interest rate swap contract designated as a cash flow hedge to hedge the interest rate associated with $14.4 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 September 30, 2015 and December 31, 2014, the Bancorp has pledged collateral to derivative counterparties in the form of cash totaling $550 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 September 30, 2015 and December 31, 2014, Washington Trust had interest rate swap contracts with commercial loan borrowers with notional amounts of $272.6 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

During 2015, the Corporation entered into risk participation agreements (“RPAs”) with other banks participating in commercial loan arrangements. Participating banks guarantee the performance on borrower-related interest rate swap contracts. RPAs are derivative financial instruments and are recorded at fair value. Changes in the fair value of the derivative assets and liabilities are recognized in earnings in the period of change.

Under a risk participation-out agreement, a derivative asset, the Corporation participates out a portion of the credit risk associated with the interest rate swap position executed with the commercial borrower, for a fee paid to the participating bank. Under a risk participation-in agreement, a derivative liability, the Corporation assumes, or participates in, a portion of the credit risk associated with the interest rate swap position with the commercial borrower, for a fee received from the other bank.

As of September 30, 2015, the notional amounts of the risk participation-out agreements and risk participation-in agreements were $25.3 million and $8.0 million, respectively.

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.