Held-to-maturity securities (“HTM”), which include any security for which the Company has the positive intent and ability to hold until maturity, are carried at historical cost adjusted for amortization of premiums and accretion of discounts. Premiums and discounts are amortized and accreted, respectively, to interest income using the constant effective yield method over the estimated life of the security. Prepayments are anticipated for mortgage-backed and SBA securities. Premiums on callable securities are amortized to their earliest call date.

Available-for-sale securities (“AFS”), which include any security for which the Company has no immediate plan to sell but which may be sold in the future, are carried at fair value. Realized gains and losses, based on specifically identified amortized cost of the individual security, are included in other income. Unrealized gains and losses are recorded, net of related income tax effects, in stockholders’ equity, further discussed below. Premiums and discounts are amortized and accreted, respectively, to interest income using the constant effective yield method over the estimated life of the security. Prepayments are anticipated for mortgage-backed and SBA securities. Premiums on callable securities are amortized to their earliest call date.


(In thousands)	Amortized Cost		Allowance for Credit Losses		Net Carrying Amount		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Held-to-Maturity

March 31, 2021
U.S. Government agencies	$	77,396	$	—	$	77,396	$	—	$	(3,757)	$	73,639
Mortgage-backed securities	47,988		—		47,988		476		(1,099)		47,365
State and political subdivisions	485,158		(1,042)		484,116		1,718		(9,188)		476,646
Other securities	576		(576)		—		44		—		44
Total HTM	$	611,118	$	(1,618)	$	609,500	$	2,238	$	(14,044)	$	597,694

December 31, 2020
Mortgage-backed securities	$	22,354	$	—	$	22,354	$	683	$	—	$	23,037
State and political subdivisions	312,416		(2,307)		310,109		8,148		(30)		318,227
Other securities	1,176		(608)		568		93		—		661
Total HTM	$	335,946	$	(2,915)	$	333,031	$	8,924	$	(30)	$	341,925


(In thousands)	Amortized Cost		Allowance for Credit Losses		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Available-for-sale

March 31, 2021
U.S. Treasury	$	600	$	—	$	—	$	—	$	600
U.S. Government agencies	511,973		—		369		(24,663)		487,679
Mortgage-backed securities	2,156,121		—		12,917		(35,952)		2,133,086
State and political subdivisions	1,570,747		(64)		25,916		(24,689)		1,571,910
Other securities	342,611		(2,390)		3,343		(8,491)		335,073
Total AFS	$	4,582,052	$	(2,454)	$	42,545	$	(93,795)	$	4,528,348

December 31, 2020
U.S. Government agencies	$	477,693	$	—	$	844	$	(1,300)	$	477,237
Mortgage-backed securities	1,374,769		—		21,261		(1,094)		1,394,936
State and political subdivisions	1,416,136		(217)		55,111		(307)		1,470,723
Other securities	128,445		(95)		2,447		(95)		130,702
Total AFS	$	3,397,043	$	(312)	$	79,663	$	(2,796)	$	3,473,598

Accrued interest receivable on HTM and AFS securities at March 31, 2021 was $3.4 million and $20.2 million, respectively, and is included in interest receivable on the consolidated balance sheets. The Company has made the election to exclude all accrued interest receivable from securities from the estimate of credit losses.

The following table summarizes the Company’s AFS investments in an unrealized loss position for which an allowance for credit loss has not been recorded as of March 31, 2021, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position:


	Less Than 12 Months				12 Months or More				Total
(In thousands)	Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses
Available-for-sale
U.S. Government agencies	$	402,235	$	(23,887)	$	49,123	$	(776)	$	451,358	$	(24,663)
Mortgage-backed securities	1,622,032		(35,949)		323		(3)		1,622,355		(35,952)
State and political subdivisions	299,613		(24,624)		90		(1)		299,703		(24,625)
Other securities	49,421		(6,101)		—		—		49,421		(6,101)
Total AFS	$	2,373,301	$	(90,561)	$	49,536	$	(780)	$	2,422,837	$	(91,341)

As of March 31, 2021, the Company’s investment portfolio included $4.5 billion of AFS securities, of which $2.4 billion, or 53.5%, were in an unrealized loss position that were not deemed to have credit losses. A portion of the unrealized losses were related to the Company’s mortgage-backed securities, which are issued and guaranteed by U.S. government-sponsored entities and agencies, and the Company’s state and political securities, specifically investments in insured fixed rate municipal bonds for which the issuers continue to make timely principal and interest payments under the contractual terms of the securities.

Furthermore, the decline in fair value for each of the above AFS securities is attributable to the rates for those investments yielding less than current market rates. Management does not believe any of the securities are impaired due to reasons of credit quality. Management believes the declines in fair value for the securities are temporary. Management does not have the intent to sell the securities, and management believes it is more likely than not the Company will not have to sell the securities before recovery of their amortized cost basis.

All mortgage-backed securities held by the Company are issued by U.S. government-sponsored entities and agencies. These securities are either explicitly or implicitly guaranteed by the U.S. government, are highly rated by major rating agencies and have a long history of no credit losses. Accordingly, no allowance for credit losses has been recorded for these securities.

Regarding securities issued by state and political subdivisions and other HTM securities, management considers (i) issuer bond ratings, (ii) historical loss rates for given bond ratings, (iii) whether issuers continue to make timely principal and interest payments under the contractual terms of the securities, (iv) internal forecasts, (v) whether or not such securities provide insurance or other credit enhancement or are pre-refunded by the issuers.


(In thousands)	State and Political Subdivisions		Other Securities		Total













Three Months Ended March 31, 2021
Held-to-Maturity
Beginning balance, January 1, 2021	$	2,307	$	608	$	2,915
Provision for credit loss expense	(1,265)		568		(697)
Securities charged-off	—		(600)		(600)
Ending balance, March 31, 2021	$	1,042	$	576	$	1,618

Available-for-sale
Beginning balance, January 1, 2021	$	217	$	95	$	312
Credit losses on securities not previously recorded	61		2,237		2,298
Reduction due to sales	—		(11)		(11)
Net decrease in allowance on previously impaired securities	(214)		69		(145)
Ending balance, March 31, 2021	$	64	$	2,390	$	2,454

Three Months Ended March 31, 2020
Held-to-Maturity
Beginning balance, January 1, 2020	$	—	$	—	$	—
Impact of ASU 2016-13 adoption	58		311		369
Provision for credit loss expense	39		1		40
Ending balance, March 31, 2020	$	97	$	312	$	409

Available-for-sale
Beginning balance, January 1, 2020	$	—	$	—	$	—
Impact of ASU 2016-13 adoption	373		—		373
Credit losses on securities not previously recorded	44		174		218
Net decrease in allowance on previously impaired securities	(322)		—		(322)
Ending balance, March 31, 2020	$	95	$	174	$	269

The provision for credit losses related to AFS securities was $2,142,000 during the three months ended March 31, 2021. During the three months ended March 31, 2020, the provision for credit losses related to AFS securities was a benefit to expense of $104,000.


	State and Political Subdivisions
(In thousands)	Not Guaranteed or Pre-Refunded		Other Credit Enhancement or Insurance		Pre-Refunded		Total		Other Securities
Aaa/AAA	$	49,354	$	17,894	$	—	$	67,248	$	—
Aa/AA	176,578		74,570		—		251,148		—
A	19,516		6,445		—		25,961		—
Not Rated	95,729		45,072		—		140,801		576
Total	$	341,177	$	143,981	$	—	$	485,158	$	576

Historical loss rates associated with securities having similar grades as those in the Company’s portfolio have generally not been significant. Pre-refunded securities, if any, have been defeased by the issuer and are fully secured by cash and/or U.S. Treasury securities held in escrow for payment to holders when the underlying call dates of the securities are reached. Securities with other credit enhancement or insurance continue to make timely principal and interest payments under the contractual terms of the securities. Accordingly, no allowance for credit losses has been recorded for these securities as there is no current expectation of credit losses related to these securities.

The amortized cost and estimated fair value by maturity of securities are shown in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities.


	Held-to-Maturity				Available-for-Sale
(In thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
One year or less	$	7,034	$	7,117	$	11,951	$	12,000
After one through five years	8,931		9,317		28,425		28,755
After five through ten years	5,695		4,556		373,751		370,817
After ten years	541,470		529,339		2,010,880		1,982,767
Securities not due on a single maturity date	47,988		47,365		2,156,121		2,133,086
Other securities (no maturity)	—		—		924		923
Total	$	611,118	$	597,694	$	4,582,052	$	4,528,348

There were approximately $5.5 million of gross realized gains and $13,000 of gross realized losses from the sale of securities during the three months ended March 31, 2021. The Company sold approximately $135.7 million of investment securities during the three months ended March 31, 2021. There were approximately $32.1 million of gross realized gains and $2,080 of gross realized losses from the sale of securities during the three months ended March 31, 2020. During the first quarter of 2020, the Company sold approximately $1.1 billion of investment securities to create additional liquidity. The income tax expense/benefit related to security gains/losses was 26.135% of the gross amounts in 2021 and 2020.