Basis of Presentation And Summary Of Significant Accounting Policies	3 Months Ended
Mar. 31, 2013
Basis of Presentation And Summary Of Significant Accounting Policies [Abstract]
Basis Of Presentation And Summary Of Significant Accounting Policies	(1.) BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations Financial Institutions, Inc., a financial holding company organized under the laws of New York State ("New York" or "NYS"), and its subsidiaries provide deposit, lending and other financial services to individuals and businesses in Central and Western New York. The Company has also expanded its indirect lending network to include relationships with franchised automobile dealers in the Capital District of New York and Northern Pennsylvania. Financial Institutions, Inc. owns all of the capital stock of Five Star Bank, a New York State chartered bank, and Five Star Investment Services, Inc., a financial services subsidiary offering noninsured investment products and investment advisory services. References to "the Company" mean the consolidated reporting entities and references to "the Bank" mean Five Star Bank. Basis of Presentation The consolidated financial statements include the accounts of Financial Institutions, Inc. and its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. The accounting and reporting policies conform to U.S. generally accepted accounting principles ("GAAP"). Certain information and footnote disclosures normally included in financial statements prepared in conformity with GAAP have been condensed or omitted pursuant to such rules and regulations. However, in the opinion of management, the accompanying consolidated financial statements reflect all adjustments of a normal and recurring nature necessary for a fair presentation of the consolidated statements of financial condition, income, comprehensive income, shareholders' equity and cash flows for the periods indicated, and contain adequate disclosure to make the information presented not misleading. Prior years' consolidated financial statements are re-classified whenever necessary to conform to the current year's presentation. These consolidated financial statements should be read in conjunction with the Company's 2012 Annual Report on Form 10-K. The results of operations for any interim periods are not necessarily indicative of the results which may be expected for the entire year. Subsequent Events The Company has evaluated events and transactions for potential recognition or disclosure through the day the financial statements were issued. Use of Estimates The preparation of these financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. Material estimates relate to the determination of the allowance for loan losses, assumptions used in the defined benefit pension plan accounting, the carrying value of goodwill and deferred tax assets, and the valuation and other than temporary impairment considerations related to the securities portfolio. Reclassifications Certain reclassifications have been made to the prior years' financial statements in order to reflect retrospective adjustments made to the balance of goodwill at December 31, 2012 to reflect the effect of these measurement period adjustments made in accordance with accounting requirements. The reclassifications had no impact on shareholders' equity or net income. Recent Accounting Pronouncements In February 2013, the Financial Accounting Standards Board issued Accounting Standards Update ("ASU") No. 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. The Update does not amend any existing requirements for reporting net income or other comprehensive income in the financial statements. ASU No. 2013-02 requires an entity to disaggregate the total change of each component of other comprehensive income (e.g., unrealized gains or losses on available-for-sale investment securities) and separately present reclassification adjustments and current period other comprehensive income. The provisions of ASU No. 2013-02 also requires that entities present either in a single note or parenthetically on the face of the financial statements, the effect of significant amounts reclassified from each component of accumulated other comprehensive income based on its source (e.g., unrealized gains or losses on available-for-sale investment securities) and the income statement line item affected by the reclassification (e.g., realized gains (losses) on sales of investment securities). If a component is not required to be reclassified to net income in its entirety (e.g., amortization of defined benefit plan items), entities would instead cross reference to the related note to the financial statements for additional information (e.g., pension footnote). The Company adopted the provisions of ASU No. 2013-02 effective January 1, 2013. As the Company provided these required disclosures in the notes to the consolidated financial statements, the adoption of ASU No. 2013-02 had no impact on the Company's consolidated statements of income and condition. See Note 8 – Accumulated Other Comprehensive Income to the consolidated financial statements for the disclosures required by ASU No. 2013-02.

(1.) BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Nature of Operations

Financial Institutions, Inc., a financial holding company organized under the laws of New York State ("New York" or "NYS"), and its subsidiaries provide deposit, lending and other financial services to individuals and businesses in Central and Western New York. The Company has also expanded its indirect lending network to include relationships with franchised automobile dealers in the Capital District of New York and Northern Pennsylvania. Financial Institutions, Inc. owns all of the capital stock of Five Star Bank, a New York State chartered bank, and Five Star Investment Services, Inc., a financial services subsidiary offering noninsured investment products and investment advisory services. References to "the Company" mean the consolidated reporting entities and references to "the Bank" mean Five Star Bank.

Basis of Presentation

The consolidated financial statements include the accounts of Financial Institutions, Inc. and its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. The accounting and reporting policies conform to U.S. generally accepted accounting principles ("GAAP"). Certain information and footnote disclosures normally included in financial statements prepared in conformity with GAAP have been condensed or omitted pursuant to such rules and regulations. However, in the opinion of management, the accompanying consolidated financial statements reflect all adjustments of a normal and recurring nature necessary for a fair presentation of the consolidated statements of financial condition, income, comprehensive income, shareholders' equity and cash flows for the periods indicated, and contain adequate disclosure to make the information presented not misleading. Prior years' consolidated financial statements are re-classified whenever necessary to conform to the current year's presentation. These consolidated financial statements should be read in conjunction with the Company's 2012 Annual Report on Form 10-K. The results of operations for any interim periods are not necessarily indicative of the results which may be expected for the entire year.

Subsequent Events

The Company has evaluated events and transactions for potential recognition or disclosure through the day the financial statements were issued.

Use of Estimates

The preparation of these financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. Material estimates relate to the determination of the allowance for loan losses, assumptions used in the defined benefit pension plan accounting, the carrying value of goodwill and deferred tax assets, and the valuation and other than temporary impairment considerations related to the securities portfolio.

Reclassifications

Certain reclassifications have been made to the prior years' financial statements in order to reflect retrospective adjustments made to the balance of goodwill at December 31, 2012 to reflect the effect of these measurement period adjustments made in accordance with accounting requirements. The reclassifications had no impact on shareholders' equity or net income.

Recent Accounting Pronouncements

In February 2013, the Financial Accounting Standards Board issued Accounting Standards Update ("ASU") No. 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. The Update does not amend any existing requirements for reporting net income or other comprehensive income in the financial statements. ASU No. 2013-02 requires an entity to disaggregate the total change of each component of other comprehensive income (e.g., unrealized gains or losses on available-for-sale investment securities) and separately present reclassification adjustments and current period other comprehensive income. The provisions of ASU No. 2013-02 also requires that entities present either in a single note or parenthetically on the face of the financial statements, the effect of significant amounts reclassified from each component of accumulated other comprehensive income based on its source (e.g., unrealized gains or losses on available-for-sale investment securities) and the income statement line item affected by the reclassification (e.g., realized gains (losses) on sales of investment securities). If a component is not required to be reclassified to net income in its entirety (e.g., amortization of defined benefit plan items), entities would instead cross reference to the related note to the financial statements for additional information (e.g., pension footnote). The Company adopted the provisions of ASU No. 2013-02 effective January 1, 2013. As the Company provided these required disclosures in the notes to the consolidated financial statements, the adoption of ASU No. 2013-02 had no impact on the Company's consolidated statements of income and condition. See Note 8 – Accumulated Other Comprehensive Income to the consolidated financial statements for the disclosures required by ASU No. 2013-02.