Employee Benefits (Policies)	12 Months Ended
Employee Benefits (Policies)	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Plans Policy	Pension benefit costs and benefit obligations incorporate various actuarial and other assumptions, including discount rates, mortality, assumed rates of return on plan assets and compensation increases. Washington Trust evaluates these assumptions annually. The discount rate is used to calculate the present value of the expected future cash flows for benefit obligations under our pension plans. As a result of the annual measurement of defined benefit pension liabilities at December 31, 2014, the projected benefit obligations increased by $14.0 million. Approximately $9.2 million of the increase was due to a decline in the discount rate in 2014, while approximately $3.8 million was the result of the adoption of new mortality assumptions reflecting increased life expectancies, that were recently issued by the Society of Actuaries. The impact of the increase in projected benefit obligations was included in actuarial loss and recognized in other comprehensive income. In September 2013, the Corporation amended its defined benefit pension plans primarily to freeze benefit accruals after a 10-year transition period ending in December 2023. As a result, the plans were remeasured in September 2013 and a curtailment was recognized, which reduced the projected benefit obligations by $4.4 million at that time. The impact of this was recognized in other comprehensive income. The assets of the qualified defined benefit pension plan trust (the “Pension Trust”) are managed to balance the needs of cash flow requirements and long-term rate of return. Cash inflow is typically comprised of invested income from portfolio holdings and Bank contributions, while cash outflow is for the purpose of paying plan benefits and certain plan expenses. As early as possible each year, the trustee is advised of the projected schedule of employer contributions and estimations of benefit payments. As a general rule, the trustee shall invest the funds so as to produce sufficient income to cover benefit payments and maintain a funded status that exceeds the regulatory requirements for tax-qualified defined benefit plans. The investment philosophy used for the Pension Trust emphasizes consistency of results over an extended market cycle, while reducing the impact of the volatility of the security markets upon investment results. The assets of the Pension Trust should be protected by substantial diversification of investments, providing exposure to a wide range of quality investment opportunities in various asset classes, with a high degree of liquidity. The investment objective with respect to the Pension Trust assets is to provide capital appreciation with a current income component. At any time, the portfolio will typically be invested in the following ranges: 50% to 70% in equities; 30% to 50% in fixed income; and 0% to 10% in cash and cash equivalents. The trustee investment manager will have authorization to invest within these ranges, making decisions based upon market conditions. Contributions The Internal Revenue Code permits flexibility in plan contributions so that normally a range of contributions is possible. The Corporation’s current funding policy has been generally to contribute the minimum required contribution and additional amounts up to the maximum deductible contribution. Fixed income bond investments should be limited to those in the top four categories used by the major credit rating agencies. High yield bond funds may be used to provide exposure to this asset class as a diversification tool provided they do not exceed 10% of the portfolio. In order to reduce the volatility of the annual rate of return of the bond portfolio, attention will be given to the maturity structure of the portfolio in the light of money market conditions and interest rate forecasts. The assets of the Pension Trust will typically have a laddered maturity structure, avoiding large concentrations in any single year. Common stock and equity holdings provide opportunities for dividend and capital appreciation returns. Holdings will be appropriately diversified by maintaining broad exposure to large-, mid- and small-cap stocks as well as international equities. Concentration in small-cap, mid-cap and international equities is limited to no more than 20%, 20% and 30% of the equity portfolio, respectively. Investment selection and mix of equity holdings should be influenced by forecasts of economic activity, corporate profits and allocation among different segments of the economy while ensuring efficient diversification. The fair value of equity securities of any one issuer will not be permitted to exceed 10% of the total fair value of equity holdings of the Pension Trust. Investments in publicly traded real estate investment trust securities and low-risk derivatives securities such as callable securities, floating rate notes, mortgage backed securities and treasury inflation protected securities, are permitted. The qualified pension plan uses fair value measurements to record fair value adjustments to the securities held in its investment portfolio. When available, the qualified pension plan uses quoted market prices to determine the fair value of securities; such items are classified as Level 1. This category includes cash equivalents, common stock and mutual funds which are exchange‑traded. Level 2 securities in the qualified pension plan include debt securities with quoted prices, which are traded less frequently than exchange-traded instruments, whose values are determined using matrix pricing with inputs that are observable in the market or can be derived principally from or corroborated by observable market data. This category includes corporate bonds, municipal bonds, obligations of U.S. government agencies and U.S. government-sponsored enterprises and mortgage backed securities issued by U.S. government agencies and U.S. government-sponsored enterprises. In certain cases where there is limited activity or less transparency around inputs to the valuation, securities may be classified as Level 3. 401(k) Plan The Corporation’s 401(k) Plan provides a specified match of employee contributions for substantially all employees. In addition, substantially all employees hired after September 30, 2007, who are ineligible for participation in the qualified defined benefit pension plan, receive a non-elective employer contribution of 4%. Defined Benefit Pension Plans The Corporation maintains a tax-qualified defined benefit pension plan for the benefit of certain eligible employees who were hired prior to October 1, 2007. The Corporation also has non-qualified retirement plans to provide supplemental retirement benefits to certain employees, as defined in the plans. The defined benefit pension plan is funded on a current basis, in compliance with the requirements of ERISA. The discount rate assumption for defined benefit pension plans is reset on the measurement date. A discount rate was selected for each plan by matching expected future benefit payments stream to a yield curve based on a selection of high‑quality fixed-income debt securities. Other Incentive Plans The Corporation maintains several non-qualified incentive compensation plans. Substantially all employees participate in one of the incentive compensation plans. Incentive plans provide for annual or more frequent payments based on individual, business line and/or corporate performance targets (measured in terms of the Corporation’s net income, earnings per share and return on equity). Total incentive based compensation amounted to $13.8 million, $13.4 million and $13.5 million in 2014, 2013 and 2012, respectively. In general, the terms of incentive plans are subject to annual renewal and may be terminated at any time by the Compensation Committee of the Board of Directors. Deferred Compensation Plan The Amended and Restated Nonqualified Deferred Compensation Plan provides supplemental retirement and tax benefits to directors and certain officers. The plan is funded primarily through pre-tax contributions made by the participants. The assets and liabilities of the Deferred Compensation Plan are recorded at fair value in the Corporation’s Consolidated Balance Sheets. The participants in the plan bear the risk of market fluctuations of the underlying assets. The expected long-term rate of return on plan assets is based on what the Corporation believes is realistically achievable based on the types of assets held by the plan and the plan’s investment practices. The assumption is updated annually, taking into account the asset allocation, historical asset return trends on the types of assets held and the current and expected economic conditions.

Disclosure of accounting policy for pension and other postretirement benefit plans. This accounting policy may address (1) the types of plans sponsored by the entity, and the benefits provided by each plan (2) groups that participate in (or are covered by) each plan (3) how plan assets, liabilities and expenses are measured, including the use of any actuaries and (4) significant assumptions used by the entity to value plan assets and liabilities and how such assumptions are derived.

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