The Company’s AFS investment portfolio is generally highly-rated or agency backed. All AFS securities were current with no securities past due or on non-accrual as of March 31, 2021 and December 31, 2020.

The amortized cost, gross unrealized gains and losses, and estimated fair values of AFS securities as of March 31, 2021 are summarized as follows (dollars in thousands):

(1)	Other bonds include asset-backed securities.

The amortized cost, gross unrealized gains and losses, and estimated fair values of AFS securities as of December 31, 2020 are summarized as follows (dollars in thousands):


	Amortized		Gross Unrealized				Estimated
	Cost		Gains		(Losses)		Fair Value
December 31, 2020
U.S. government and agency securities	$	13,009	$	437	$	(52)	$	13,394
Obligations of states and political subdivisions		786,466		50,878		(18)		837,326
Corporate and other bonds ⁽¹⁾		148,747		2,430		(99)		151,078
Commercial mortgage-backed securities
Agency		321,015		16,277		(2)		337,290
Non-agency		51,244		167		(17)		51,394
Total commercial mortgage-backed securities		372,259		16,444		(19)		388,684
Residential mortgage-backed securities
Agency		1,012,237		31,816		(1,946)		1,042,107
Non-agency		104,904		1,507		(206)		106,205
Total residential mortgage-backed securities		1,117,141		33,323		(2,152)		1,148,312
Other securities		1,625		—		—		1,625
Total AFS securities	$	2,439,247	$	103,512	$	(2,340)	$	2,540,419

⁽¹⁾ Other bonds include asset-backed securities

The following table shows the gross unrealized losses and fair value of the Company’s AFS securities with unrealized losses for which an ACL has not been recorded at March 31, 2021 and December 31, 2020 and that are not deemed to be impaired as of those dates. These are aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position (dollars in thousands).


	Less than 12 months				More than 12 months				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Losses		Value		Losses		Value		Losses
March 31, 2021
U.S. government and agency securities	$	—	$	—	$	4,899	$	(47)	$	4,899	$	(47)
Obligations of states and political subdivisions		271,172		(4,956)		—		—		271,172		(4,956)
Corporate and other bonds⁽¹⁾		42,612		(237)		4,785		(6)		47,397		(243)
Commercial mortgage-backed securities
Agency		65,708		(1,614)		359		(1)		66,067		(1,615)
Non-agency		26,736		(110)		—		—		26,736		(110)
Total commercial mortgage-backed securities		92,444		(1,724)		359		(1)		92,803		(1,725)
Residential mortgage-backed securities
Agency		558,523		(13,650)		1,175		(18)		559,698		(13,668)
Non-agency		36,031		(491)		10,070		(21)		46,101		(512)
Total residential mortgage-backed securities		594,554		(14,141)		11,245		(39)		605,799		(14,180)
Total AFS securities	$	1,000,782	$	(21,058)	$	21,288	$	(93)	$	1,022,070	$	(21,151)

December 31, 2020
U.S. government and agency securities	$	—	$	—	$	5,456	$	(52)	$	5,456	$	(52)
Obligations of states and political subdivisions		5,091		(18)		—		—		5,091		(18)
Corporate and other bonds⁽¹⁾		17,946		(52)		10,698		(47)		28,644		(99)
Commercial mortgage-backed securities
Agency		5,893		(2)		376		—		6,269		(2)
Non-agency		17,654		(17)		—		—		17,654		(17)
Total commercial mortgage-backed securities		23,547		(19)		376		—		23,923		(19)
Residential mortgage-backed securities
Agency		219,388		(1,944)		1,055		(2)		220,443		(1,946)
Non-agency		36,942		(206)		—		—		36,942		(206)
Total residential mortgage-backed securities		256,330		(2,150)		1,055		(2)		257,385		(2,152)
Total AFS securities	$	302,914	$	(2,239)	$	17,585	$	(101)	$	320,499	$	(2,340)

⁽¹⁾ Other bonds includes asset-backed securities.

As of March 31, 2021, there were $21.3 million, or 12 instances, of individual AFS securities that had been in a continuous loss position for more than 12 months and had an aggregate unrealized loss of $93,000. As of December 31, 2020, there were $17.6 million, or 15 instances, of individual securities that had been in a continuous loss position for more than 12 months and had an aggregate unrealized loss of $101,000.

The Company has evaluated AFS securities in an unrealized loss position for credit related impairment at March 31, 2021 and December 31, 2020 and concluded no impairment existed based on several factors which included: (1) the majority of these securities are of high credit quality, (2) unrealized losses are primarily the result of market volatility, (3) the contractual terms of the investments do not permit the issuer(s) to settle the securities at a price less than the cost basis of each investment, (4) issuers continue to make timely principal and interest payments, and (5) the Company does not intend to sell any of the investments and the accounting standard of “more likely than not” has not been met for the Company to be required to sell any of the investments before recovery of its amortized cost basis.

Additionally, the majority of the Company’s mortgage-backed securities are issued by FNMA, FHLMC, and GNMA and do not have credit risk given the implicit and explicit government guarantees associated with these agencies. In addition, the non-agency mortgage-backed and asset-backed securities generally received a 20% SSFA rating.

The following table presents the amortized cost and estimated fair value of AFS securities as of March 31, 2021 and December 31, 2020, by contractual maturity. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties (dollars in thousands).


	March 31, 2021				December 31, 2020
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	18,007	$	18,168	$	19,875	$	19,997
Due after one year through five years		166,575		172,723		161,448		169,103
Due after five years through ten years		233,566		239,838		235,021		242,791
Due after ten years		2,221,915		2,266,314		2,022,903		2,108,528
Total AFS securities	$	2,640,063	$	2,697,043	$	2,439,247	$	2,540,419

Refer to Note 7 "Commitments and Contingencies" for information regarding the estimated fair value of AFS securities that were pledged to secure public deposits, repurchase agreements, and for other purposes as permitted or required by law as of March 31, 2021 and December 31, 2020.

Held to Maturity

The Company’s HTM investment portfolio primarily consists of highly-rated municipal securities and the estimated credit loss inherent in the portfolio is currently immaterial. The Company’s HTM securities were all current, with no securities past due or on non-accrual at March 31, 2021 and December 31, 2020.

The Company reports HTM securities on the Company’s Consolidated Balance Sheets at carrying value. Carrying value is amortized cost, which includes any unamortized unrealized gains and losses recognized in accumulated other comprehensive income prior to reclassifying the securities from AFS securities to HTM securities. Investment securities transferred into the HTM category from the AFS category are recorded at fair value at the date of transfer. The unrealized holding gain or loss at the date of transfer is retained in accumulated other comprehensive income and in the carrying value of the HTM securities. Such unrealized gains or losses are accreted over the remaining life of the security with no impact on future net income.

The carrying value, gross unrealized gains and losses, and estimated fair values of HTM securities as of March 31, 2021 are summarized as follows (dollars in thousands):

Carrying

Gross Unrealized

Estimated

Value

Gains

(Losses)

Fair Value

March 31, 2021

U.S. government and agency securities

2,676

—

(31)

2,645

Obligations of states and political subdivisions

535,634

62,880

—

598,514

Commercial mortgage-backed securities

Agency

5,265

(66)

5,200

Non-agency

—

Total commercial mortgage-backed securities

5,265

(66)

5,200

Total held-to-maturity securities

543,575

62,881

(97)

606,359

The carrying value, gross unrealized gains and losses, and estimated fair values of HTM securities as of December 31, 2020 are summarized as follows (dollars in thousands):


	Carrying		Gross Unrealized				Estimated
	Value		Gains		(Losses)		Fair Value
December 31, 2020
U.S. government and agency securities	$	2,751	$	—	$	(18)	$	2,733
Obligations of states and political subdivisions		536,767		74,978		—		611,745
Commercial mortgage-backed securities
Agency		5,333		4		(50)		5,287
Non-agency		—		—		—		—
Total commercial mortgage-backed securities		5,333		4		(50)		5,287
Total held-to-maturity securities	$	544,851	$	74,982	$	(68)	$	619,765

Credit Quality Indicators & Allowance for Credit Losses - HTM

For HTM securities, the Company evaluates the credit risk of its securities on at least a quarterly basis. The Company estimates expected credit losses on HTM debt securities on an individual basis based on the PD/LGD methodology primarily using security-level credit ratings. The Company’s HTM securities ACL was immaterial at March 31, 2021 and December 31, 2020. The primary indicators of credit quality for the Company’s HTM portfolio are security type and credit rating, which is influenced by a number of factors including obligor cash flow, geography, seniority, and others. The Company’s only HTM securities with credit risk are obligations of states and political subdivisions.

The following table presents the amortized cost of HTM securities as of March 31, 2021 and December 31, 2020 by security type and credit rating (dollars in thousands):


	U.S. Government and Agency		Obligations of states and political		Mortgage-backed		Total HTM
	securities		subdivisions		securities		securities
March 31, 2021
Credit Rating:
AAA/AA/A	$	—	$	531,203	$	—	$	531,203
Not Rated - Agency⁽¹⁾		2,676		—		5,265		7,941
Not Rated - Non-Agency		—		4,431		—		4,431
Total	$	2,676	$	535,634	$	5,265	$	543,575
December 31, 2020
Credit Rating:
AAA/AA/A	$	—	$	532,157	$	—	$	532,157
Not Rated - Agency⁽¹⁾		2,751		—		5,333		8,084
Not Rated - Non-Agency		—		4,610		—		4,610
Total	$	2,751	$	536,767	$	5,333	$	544,851

⁽¹⁾ Generally considered not to have credit risk given the government guarantees associated with these agencies

The following table presents the amortized cost and estimated fair value of HTM securities as of March 31, 2021 and December 31, 2020, by contractual maturity. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties (dollars in thousands).


	March 31, 2021				December 31, 2020
	Carrying		Estimated		Carrying		Estimated
	Value		Fair Value		Value		Fair Value
Due in one year or less	$	1,441	$	1,449	$	1,443	$	1,460
Due after one year through five years		8,518		8,786		8,577		8,893
Due after five years through ten years		1,680		1,719		1,744		1,805
Due after ten years		531,936		594,405		533,087		607,607
Total HTM securities	$	543,575	$	606,359	$	544,851	$	619,765

Refer to Note 7 "Commitments and Contingencies" for information regarding the estimated fair value of HTM securities that were pledged to secure public deposits as permitted or required by law as of March 31, 2021 and December 31, 2020.

Restricted Stock, at cost

Due to restrictions placed upon the Bank’s common stock investment in the Federal Reserve Bank and FHLB, these securities have been classified as restricted equity securities and carried at cost. These restricted securities are not subject to the investment security classifications and are included as a separate line item on the Company’s Consolidated Balance Sheets. The FHLB required the Bank to maintain stock in an amount equal to 3.75% and 4.25% of outstanding borrowings at March 31, 2021 and December 31, 2020, respectively, as well as a specific percentage of the Bank’s total assets. The Federal Reserve Bank required the Bank to maintain stock with a par value equal to 6% of the Bank’s outstanding capital at both March 31, 2021 and December 31, 2020. Restricted equity securities consist of Federal Reserve Bank stock in the amount of $67.0 million for March 31, 2021 and December 31, 2020 and FHLB stock in the amount of $9.8 million and $27.8 million as of March 31, 2021 and December 31, 2020, respectively.

Realized Gains and Losses

The following table presents the gross realized gains and losses on and the proceeds from the sale of securities during the three months ended March 31, 2021 and 2020 (dollars in thousands).


	Three Months Ended		Three Months Ended
	March 31, 2021		March 31, 2020
Realized gains (losses):
Gross realized gains	$	138	$	2,164
Gross realized losses		(60)		(228)
Net realized gains	$	78	$	1,936

Proceeds from sales of securities	$	45,436	$	120,701