Held-to-maturity securities, 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 yield method over the period to maturity.

Available-for-sale securities, 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 yield method over the period to maturity.


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

June 30, 2020
Mortgage-backed securities	$	25,980	$	—	$	25,980	$	798	$	(1)	$	26,777
State and political subdivisions	24,872		(95)		24,777		1,125		(2)		25,900
Other securities	1,175		(212)		963		111		—		1,074
Total HTM	$	52,027	$	(307)	$	51,720	$	2,034	$	(3)	$	53,751


(In thousands)	Amortized Cost		Allowance for Credit Losses		Net Carrying Amount		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
December 31, 2019
Mortgage-backed securities	$	10,796	$	—	$	10,796	$	71	$	(59)	$	10,808
State and political subdivisions	27,082		—		27,082		849		—		27,931
Other securities	3,049		—		3,049		67		—		3,116
Total HTM	$	40,927	$	—	$	40,927	$	987	$	(59)	$	41,855


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

June 30, 2020
U.S. Government agencies	$	210,496	$	—	$	1,416	$	(991)	$	210,921
Mortgage-backed securities	1,125,484		—		28,804		(202)		1,154,086
State and political subdivisions	1,015,625		(371)		39,510		(696)		1,054,068
Other securities	76,943		(238)		1,354		(238)		77,821
Total AFS	$	2,428,548	$	(609)	$	71,084	$	(2,127)	$	2,496,896

December 31, 2019
U.S. Treasury	$	449,729	$	—	$	112	$	(112)	$	449,729
U.S. Government agencies	194,207		—		1,313		(1,271)		194,249
Mortgage-backed securities	1,738,584		—		8,510		(4,149)		1,742,945
State and political subdivisions	860,539		—		20,983		(998)		880,524
Other securities	20,092		—		822		(18)		20,896
Total AFS	$	3,263,151	$	—	$	31,740	$	(6,548)	$	3,288,343

Accrued interest receivable on HTM and AFS securities at June 30, 2020 was $247,000 and $12.7 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 June 30, 2020, 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	$	3,209	$	(3)	$	56,007	$	(988)	$	59,216	$	(991)
Mortgage-backed securities	47,380		(161)		4,266		(41)		51,646		(202)
State and political subdivisions	30,468		(324)		388		(1)		30,856		(325)
Total AFS	$	81,057	$	(488)	$	60,661	$	(1,030)	$	141,718	$	(1,518)

As of June 30, 2020, the Company’s investment portfolio included $2.5 billion of AFS securities, of which $141.7 million, or 5.7%, were in an unrealized loss position that are 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 meaning 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 of the 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 pre-refunded by the issuers.


(In thousands)	State and Political Subdivisions		Other Securities		Total
Three Months Ended June 30, 2020
Held-to-Maturity
Beginning balance, April 1, 2020	$	97	$	312	$	409
Provision for credit loss expense	(2)		(100)		(102)
Ending balance, June 30, 2020	$	95	$	212	$	307

Available-for-sale
Beginning balance, April 1, 2020	$	95	$	174	$	269
Credit losses on securities not previously recorded	370		160		530
Net increase (decrease) in allowance on previously impaired securities	(94)		(96)		(190)
Ending balance, June 30, 2020	$	371	$	238	$	609

Six Months Ended June 30, 2020
Held-to-Maturity
Beginning balance, January 1, 2020	$	—	$	—	$	—
Impact of ASU 2016-13 adoption	58		311		369
Provision for credit loss expense	37		(99)		(62)
Ending balance, June 30, 2020	$	95	$	212	$	307

Available-for-sale
Beginning balance, January 1, 2020	$	—	$	—	$	—
Impact of ASU 2016-13 adoption	373		—		373
Credit losses on securities not previously recorded	77		192		269
Reduction due to sales	(142)		—		(142)
Net increase (decrease) in allowance on previously impaired securities	63		46		109
Ending balance, June 30, 2020	$	371	$	238	$	609


	State and Political Subdivisions
(In thousands)	Not Guaranteed or Pre-Refunded		Other Credit Enhancement or Insurance		Pre-Refunded		Total		Other Securities
Aaa/AAA	$	2,112	$	—	$	—	$	2,112	$	—
Aa/AA	11,512		5,922		—		17,434		—
A	961		1,147		—		2,108		—
Not Rated	2,849		369		—		3,218		1,175
Total	$	17,434	$	7,438	$	—	$	24,872	$	1,175

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.


	Three Months Ended June 30,						Six Months Ended June 30,
(In thousands)	2020		2019		2020		2019
Taxable:
Held-to-maturity	$	288	$	289	$	459	$	727
Available-for-sale	7,086		10,777		19,667		22,297

Non-taxable:
Held-to-maturity	68		89		140		1,251
Available-for-sale	6,031		4,511		12,150		7,672
Total	$	13,473	$	15,666	$	32,416	$	31,947

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	$	4,928	$	4,962	$	15,006	$	15,077
After one through five years	15,201		15,793		35,995		36,348
After five through ten years	5,918		6,219		203,777		205,627
After ten years	—		—		1,047,772		1,084,495
Securities not due on a single maturity date	25,980		26,777		1,125,484		1,154,086
Other securities (no maturity)	—		—		514		1,263
Total	$	52,027	$	53,751	$	2,428,548	$	2,496,896

The carrying value, which approximates the fair value, of securities pledged as collateral, to secure public deposits and for other purposes, amounted to $1.38 billion at June 30, 2020 and $1.73 billion at December 31, 2019.

There were approximately $391,000 of gross realized gains and $1,000 of gross realized losses from the sale of securities during the three months ended June 30, 2020, and approximately $32.5 million of gross realized gains and $2,600 of gross realized losses from the sale of securities during the six months ended June 30, 2020. During the first half of 2020, the Company sold approximately $1.2 billion of investment securities to create additional liquidity. There were approximately $2.8 million of gross realized gains and no gross realized losses from the sale of securities during the three months ended June 30, 2019, and approximately $5.6 million of gross realized gains and no gross realized losses from the sale of securities during the six months ended June 30, 2019. The income tax expense/benefit related to security gain/losses was 26.135% of the gross amounts in 2020 and 2019.