Note 2 — Securities

The following is a summary of securities available for sale as of December 31, 2020 and 2019:

The amortized cost and estimated fair value of securities as of December 31, 2020, 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, 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 an at least quarterly basis. This assessment took into account the credit quality of these debt securities and determined that since all were 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, no credit impairment had occurred.

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

In January 2016, FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (Topic 825). This new guidance, among other provisions, amends accounting related to the classification and measurement of investments in equity securities. We adopted this guidance, as required, in the first quarter of 2018. ASU 2016-01 requires the amounts reported in accumulated other comprehensive income for equity securities that exist as of the date of adoption previously classified as available-for-sale be reclassified to retained earnings. The Company reduced the balance of securities by $529,000 as of January 1, 2018, representing the loss related to all of our mutual fund equity securities, which resulted in a net reduction of retained earnings of $382,000 and an increase of $147,000 in net deferred tax assets based on the transition requirements of this standard.

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 sale of securities that had previously been recognized as net unrealized gains of $586,000 in comprehensive income. For the year ended December 31, 2018, the Company recorded $870,000 in net realized losses from the sale of securities that had previously been recognized as net unrealized losses of $413,000 in comprehensive income. This included sale of all of the Company's mutual fund equity securities with gross realized losses of $957,000. The Company recorded a $428,000 net loss in earnings resulting from the sale of these securities. The remaining loss of $529,000 related to these sold securities was recorded as a transition adjustment upon adoption of ASU 2016-01 as of the beginning of the period as described in the previous paragraph.

Securities available for sale with market values of $27.3 million and $30.2 million as of December 31, 2020 and 2019, 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 2020, 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.