The following tables present the amortized cost, the gross unrealized gains and losses and the fair value of the Company’s debt securities:


	September 30, 2023
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains	Gross Unrealized Losses	Fair Value
Available-for-sale
U.S. government and federal agency	$	485,496	13	(41,364)	444,145
U.S. government sponsored enterprises	321,532		—	(31,701)	289,831
State and local governments	102,702		96	(6,085)	96,713
Corporate bonds	27,021		—	(1,117)	25,904
Residential mortgage-backed securities	3,281,286		2	(470,394)	2,810,894
Commercial mortgage-backed securities	1,192,450		129	(118,328)	1,074,251
Total available-for-sale	$	5,410,487	240	(668,989)	4,741,738
Held-to-maturity
U.S. government and federal agency	851,751		—	(93,899)	757,852
State and local governments	1,657,628		63	(311,437)	1,346,254
Residential mortgage-backed securities	1,044,426		—	(110,065)	934,361
Total held-to-maturity	3,553,805		63	(515,401)	3,038,467
Total debt securities	$	8,964,292	303	(1,184,390)	7,780,205


	December 31, 2022
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains	Gross Unrealized Losses	Fair Value
Available-for-sale
U.S. government and federal agency	$	487,320	23	(42,616)	444,727
U.S. government sponsored enterprises	320,157		—	(32,793)	287,364
State and local governments	137,033		709	(4,749)	132,993
Corporate bonds	27,101		—	(992)	26,109
Residential mortgage-backed securities	3,706,427		6	(439,092)	3,267,341
Commercial mortgage-backed securities	1,252,065		347	(103,639)	1,148,773
Total available-for-sale	$	5,930,103	1,085	(623,881)	5,307,307
Held-to-maturity
U.S. government and federal agency	846,046		—	(83,796)	762,250
State and local governments	1,682,640		1,045	(248,233)	1,435,452
Residential mortgage-backed securities	1,186,366		—	(109,276)	1,077,090
Total held-to-maturity	3,715,052		1,045	(441,305)	3,274,792
Total debt securities	$	9,645,155	2,130	(1,065,186)	8,582,099

The following table presents the amortized cost and fair value of available-for-sale and held-to-maturity debt securities by contractual maturity at September 30, 2023. Actual maturities may differ from expected or contractual maturities since some issuers have the right to prepay obligations with or without prepayment penalties.


	September 30, 2023
	Available-for-Sale			Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Fair Value	Amortized Cost	Fair Value
Due within one year	$	1,315	1,302	4,558	4,533
Due after one year through five years	856,275		782,020	924,257	827,398
Due after five years through ten years	38,723		36,427	172,780	159,696
Due after ten years	40,438		36,844	1,407,784	1,112,479
	936,751		856,593	2,509,379	2,104,106
Mortgage-backed securities 1	4,473,736		3,885,145	1,044,426	934,361
Total	$	5,410,487	4,741,738	3,553,805	3,038,467

Proceeds from sales and calls of debt securities and the associated gains and losses that have been included in earnings are listed below:


	Three Months ended			Nine Months ended
(Dollars in thousands)	September 30, 2023		September 30, 2022	September 30, 2023	September 30, 2022
Available-for-sale
Proceeds from sales and calls of debt securities	$	410	16,745	31,695	88,011
Gross realized gains 1	—		15	145	795
Gross realized losses 1	—		—	(176)	(15)
Held-to-maturity
Proceeds from calls of debt securities	4,735		3,885	15,205	26,230
Gross realized gains 1	1		25	10	54
Gross realized losses 1	(66)		(125)	(181)	(733)

In assessing whether a credit loss existed on available-for-sale debt securities with unrealized losses, the Company compared the present value of cash flows expected to be collected from the debt securities with the amortized cost basis of the debt securities. In addition, the following factors were evaluated individually and collectively in determining the existence of expected credit losses:

•the overall deal and payment structure of the debt securities, including the investor entity’s position within the structure, underlying obligors, financial condition and near-term prospects of the issuer, including specific events which may affect the issuer’s operations or future earnings, and credit support or enhancements; and

The following table summarizes available-for-sale debt securities that were in an unrealized loss position for which an ACL has not been recorded, based on the length of time the individual securities have been in an unrealized loss position. The number of available-for-sale debt securities in an unrealized position is also disclosed.


	September 30, 2023
	Number of Securities	Less than 12 Months			12 Months or More		Total
(Dollars in thousands)		Fair Value		Unrealized Loss	Fair Value	Unrealized Loss	Fair Value	Unrealized Loss
Available-for-sale
U.S. government and federal agency	57	$	2,724	(40)	437,769	(41,324)	440,493	(41,364)
U.S. government sponsored enterprises	14	—		—	289,831	(31,701)	289,831	(31,701)
State and local governments	108	17,903		(438)	62,015	(5,647)	79,918	(6,085)
Corporate bonds	5	—		—	25,028	(1,117)	25,028	(1,117)
Residential mortgage-backed securities	414	1,598		(79)	2,809,172	(470,315)	2,810,770	(470,394)
Commercial mortgage-backed securities	159	57,493		(3,405)	1,000,441	(114,923)	1,057,934	(118,328)
Total available-for-sale	757	$	79,718	(3,962)	4,624,256	(665,027)	4,703,974	(668,989)


	December 31, 2022
	Number of Securities	Less than 12 Months			12 Months or More		Total
(Dollars in thousands)		Fair Value		Unrealized Loss	Fair Value	Unrealized Loss	Fair Value	Unrealized Loss
Available-for-sale
U.S. government and federal agency	56	$	4,150	(64)	435,375	(42,552)	439,525	(42,616)
U.S. government sponsored enterprises	14	—		—	287,364	(32,793)	287,364	(32,793)
State and local governments	121	71,512		(2,109)	20,753	(2,640)	92,265	(4,749)
Corporate bonds	5	25,146		(992)	—	—	25,146	(992)
Residential mortgage-backed securities	441	301,548		(24,581)	2,965,512	(414,511)	3,267,060	(439,092)
Commercial mortgage-backed securities	157	673,102		(41,984)	435,176	(61,655)	1,108,278	(103,639)
Total available-for-sale	794	$	1,075,458	(69,730)	4,144,180	(554,151)	5,219,638	(623,881)

With respect to severity, the majority of available-for-sale debt securities with unrealized loss positions at September 30, 2023 have unrealized losses as a percentage of book value of less than five percent. A substantial portion of such securities were issued by Federal National Mortgage Association (“Fannie Mae”), Federal Home Loan Mortgage Corporation (“Freddie Mac”), Government National Mortgage Association (“Ginnie Mae”) and other agencies of the U.S. government or have credit ratings issued by one or more of the NRSRO entities in the four highest credit rating categories. All of the Company’s available-for-sale debt securities with unrealized loss positions at September 30, 2023 have been determined to be investment grade.

The Company did not have any past due available-for-sale debt securities as of September 30, 2023 and December 31, 2022, respectively. Accrued interest receivable on available-for-sale debt securities totaled $9,694,000 and $10,518,000 at September 30, 2023, and December 31, 2022, respectively, and was excluded from the estimate of credit losses.

Based on an analysis of its available-for-sale debt securities with unrealized losses as of September 30, 2023, the Company determined the decline in value was unrelated to credit losses and was primarily the result of changes in interest rates and market spreads subsequent to acquisition. The fair value of the debt securities is expected to recover as payments are received and the debt securities approach maturity. In addition, as of September 30, 2023, management determined it did not intend to sell available-for-sale debt securities with unrealized losses, and there was no expected requirement to sell such securities before recovery of their amortized cost. As a result, no ACL was recorded on available-for-sale debt securities at September 30, 2023. As part of this determination, the Company considered contractual obligations, regulatory constraints, liquidity, capital, asset/liability management and securities portfolio objectives and whether or not any of the Company’s investment securities were managed by third-party investment funds.

The Company measured expected credit losses on held-to-maturity debt securities on a collective basis by major security type and NRSRO credit ratings, which is the Company’s primary credit quality indicator for state and local government securities. The estimate of expected credit losses considered historical credit loss information that was adjusted for current conditions as well as reasonable and supportable forecasts. The following table summarizes the amortized cost of held-to-maturity municipal bonds aggregated by NRSRO credit rating:


(Dollars in thousands)	September 30, 2023		December 31, 2022
Municipal bonds held-to-maturity
S&P: AAA / Moody’s: Aaa	$	429,432	430,542
S&P: AA+, AA, AA- / Moody’s: Aa1, Aa2, Aa3	1,180,898		1,206,441
S&P: A+, A, A- / Moody’s: A1, A2, A3	37,337		37,162

Not rated by either entity	9,961		8,495

Total municipal bonds held-to-maturity	$	1,657,628	1,682,640

The Company’s municipal bonds in the held-to-maturity debt securities portfolio is primarily comprised of general obligation and revenue bonds with NRSRO ratings in the four highest credit rating categories. All of the Company’s municipal bonds that are classified as held-to-maturity debt securities at September 30, 2023 have been determined to be investment grade. Held-to-maturity debt securities included in the Company’s U.S. government and federal agency and residential mortgage-backed security categories are issued and guaranteed by the U.S. Treasury, Fannie Mae, Freddie Mac, Ginnie Mae and other agencies of the U.S. government are considered to be zero-loss securities. This determination is in consideration of the explicit and implicit guarantees by the US Government, the US Government’s ability to print its own currency, a history of no credit losses by the US Government and noted agencies and the current economic and financial condition of the United States and US Government providing no indication the zero-loss determination is unjustified.

As of September 30, 2023 and December 31, 2022, the Company did not have any held-to-maturity debt securities past due. Accrued interest receivable on held-to-maturity debt securities totaled $21,890,000 and $17,524,000 at September 30, 2023 and December 31, 2022, respectively, and were excluded from the estimate of credit losses.

Based on the Company’s evaluation, an insignificant amount of credit losses is expected on the held-to-maturity debt securities portfolio; therefore, no ACL was recorded at September 30, 2023 or December 31, 2022.