Note 2 — Securities

The following is a summary of securities available for sale as of December 31, 2021 and 2020:

The amortized cost and estimated fair value of securities as of December 31, 2021, by contractual or expected maturity, are shown below. Collateralized mortgage obligations are included in the table shown below based on their expected maturities. All other securities are included based on their contractual maturities.

The following table summarizes debt securities available-for-sale in an unrealized loss position for which an allowance for credit losses has not been recorded at December 31, 2021 and 2020, aggregated by major security type and length of time in a continuous unrealized loss position:

The Company evaluates its available-for-sale securities portfolio for impairment on a quarterly basis. This assessment takes into account the changes in the credit quality of these debt securities since acquisition and the likelihood of a credit loss occurring over the life of the securities. In the event that a credit loss is expected to occur in the future, an allowance is established and a corresponding credit loss is recognized. Based on this analysis, the Company determined that no credit losses are expected to be realized on the tax-exempt municipal bond portfolio. The remainder of the securities portfolio consists of U.S. Treasury obligations, U.S. government agency securities, and U.S. government sponsored agency securities, all of which have the backing of the U.S. government, and are therefore not expected to incur credit losses.

Realized gains and losses on sales of securities and proceeds from sales of securities were as follows for the periods indicated:

For the year ended December 31, 2021, the Company recorded $499,000 in net realized losses from sale of securities that had previously been recognized as net unrealized losses of $123,000 in comprehensive income.

For the year ended December 31, 2020, the Company recorded $15.7 million in net realized gains from sale of securities that had previously been recognized as net unrealized gains of $15.3 million in comprehensive income. For the year ended December 31, 2019, the Company recorded $1.3 million in net realized gains from the sale of securities that had previously been recognized as net unrealized losses of $586,000 in comprehensive income.

Securities available for sale with market values of $34.7 million and $27.3 million as of December 31, 2021 and 2020, respectively, were pledged to secure advances from the Federal Reserve Bank, Discount Window facility, and for other purposes as required or permitted by law.

At year-end 2021, there were no holdings of securities of any one issuer, other than the U.S. government and its agencies in an amount greater than 10 percent of shareholders’ equity.