The amortized cost and estimated fair value of available for sale (“AFS”) securities segregated by contractual maturity at December 31, 2020 are presented below. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. Mortgage-backed securities are shown in total, as their maturities are highly variable.

The following table summarizes proceeds from the sale of AFS securities and realized gains and losses:

Securities with unrealized losses, segregated by the duration of their continuous unrealized loss positions, are summarized as follows:

A summary of securities pledged as collateral for certain deposits and borrowing arrangements as of the years ended December 31, 2020 and December 31, 2019 is as follows:

(1)	The Bank pledged securities as collateral for certain borrowing arrangements with the Federal Home Loan Bank of Boston and Federal Reserve Bank of Boston.

Securities Impairment

As a part of the Company’s ongoing security monitoring process, the Company identifies securities in an unrealized loss position that could potentially be other-than-temporarily impaired. For the twelve months ended December 31, 2020, 2019 and 2018 the Company did not record any other-than-temporary impairment (“OTTI”) losses.

The following table presents the remaining amount of historical credit losses on debt securities and changes reflected in the statement of income:


	Twelve Months Ended December 31,
(in thousands)	2020		2019		2018
Estimated credit losses as of prior year-end	$	1,697	$	1,697	$	1,697
Reductions for securities paid off during the period		—		—		—
Estimated credit losses at end of the period	$	1,697	$	1,697	$	1,697

The Company expects to recover its amortized cost basis on all debt securities in its AFS portfolio, as unrealized losses are the result of changes in the interest rate environment and other market factors. Furthermore, the Company does not intend to sell nor does it anticipate that it will be required to sell any of its securities in an unrealized loss position as of December 31, 2020, prior to this recovery. The Company’s ability and intent to hold these securities until recovery is supported by the Company’s strong capital and liquidity positions as well as its historically low portfolio turnover.

The following summarizes, by investment security type, the basis for the conclusion that the debt securities in an unrealized loss position within the Company’s AFS were not other-than-temporarily impaired at December 31, 2020:

US Government-sponsored enterprises

35 out of the total 571 securities in the Company’s portfolios of AFS US Government-sponsored enterprises were in unrealized loss positions. Aggregate unrealized losses represented 1.04% of the amortized cost of securities in unrealized loss positions. The FNMA and FHLMC guarantee the contractual cash flows of all of the Company’s US Government- sponsored enterprises. The securities are investment grade rated and there were no material underlying credit downgrades during the year. All securities are performing.

US Government agencies

10 out of the total 159 securities in the Company’s portfolios of AFS US Government agency securities were in unrealized loss positions. Aggregate unrealized losses represented 1.14% of the amortized cost of securities in unrealized loss positions. The Government National Mortgage Association (“GNMA”) guarantees the contractual cash flows of all of the Company’s US government agency securities. The securities are rated investment grade and there were no material underlying credit downgrades during the year. All securities are performing.

Private-label

9 of the total 16 securities in the Company’s portfolio of AFS private-label mortgage-backed securities were in unrealized loss positions. Aggregate unrealized losses represented 0.72% of the amortized cost of securities in unrealized loss positions. Based upon the foregoing considerations, and the expectation that the Company will receive all of the future contractual cash flows related to the amortized cost on these securities, the Company does not consider there to be any additional other-than-temporary impairment with respect to these securities.

Obligations of states and political subdivisions thereof

2 of the total 142 securities in the Company’s portfolio of AFS municipal bonds and obligations were in unrealized loss positions. Aggregate unrealized losses represented 0.12% of the amortized cost of securities in unrealized loss positions. The Company continually monitors the municipal bond sector of the market carefully and periodically evaluates the appropriate level of exposure to the market. At this time, the Company believes the bonds in this portfolio carry minimal risk of default and the Company is appropriately compensated for that risk. There were no material underlying credit downgrades during the year. All securities are performing.

Corporate bonds

11 of the total 33 securities in the Company’s portfolio of AFS corporate bonds were in an unrealized loss position. The aggregate unrealized loss represents 2.45% of the amortized cost of securities in unrealized loss positions. The Company reviews the financial strength of all of these bonds and has concluded that the amortized cost remains supported by the expected future cash flows of these securities.