Note 2 — Securities

The following is a summary of securities available for sale as of the dates indicated:

The amortized cost and estimated fair value of securities as of September 30, 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 Company evaluates its available-for-sales securities portfolio for impairment on an at least quarterly basis. This assessment takes 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, they all have the backing of the U.S. government, and thus no credit impairment is expected.

Gross unrealized losses on securities available for sale, the estimated fair value of the related securities and the number of securities aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, were as follows as of September 30, 2020 and December 31, 2019:

The unrealized losses in the U.S. government agency and sponsored agency obligations, were caused by fluctuations in interest rates. These securities are not deemed to have credit risk due to their long history with no credit losses, and the explicit guarantee of the U.S. government of timely payment of principal and interest to investors. The Company does not intend to sell the securities and it is not more likely than not that it will be required to sell them before recovery of their amortized cost.

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

During the three months ended September 30, 2020 and 2019, there were no gains or losses in earnings resulting from the sale of securities.

During the nine months ended September 30, 2020, there were $15.7 million in net gains in earnings resulting from the sale of $495.6 million of securities previously recorded with $15.3 million unrealized gains in accumulated other comprehensive income.  During the nine months ended September 30, 2019, there were $1.3 million in net gains in earnings resulting from the sale of $113.3 million of securities, which had $586,000 in previously recorded unrealized gains in accumulated other comprehensive income. 

Securities available for sale with market values of $35.0 million and $30.2 million as of September 30, 2020 and 2019, respectively, were pledged to secure borrowings from the Federal Reserve Bank (“FRB”) Discount Window.