
	December 31, 2021
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains	Gross Unrealized Losses	Fair Value
Available-for-sale
U.S. government and federal agency	$	1,356,171	174	(9,596)	1,346,749
U.S. government sponsored enterprises	241,687		2	(996)	240,693
State and local governments	461,414		27,567	(123)	488,858
Corporate bonds	175,697		5,072	(17)	180,752
Residential mortgage-backed securities	5,744,505		9,420	(54,266)	5,699,659
Commercial mortgage-backed securities	1,195,949		25,882	(7,693)	1,214,138
Total available-for-sale	$	9,175,423	68,117	(72,691)	9,170,849
Held-to-maturity
State and local governments	1,199,164		22,878	(1,159)	1,220,883
Total held-to-maturity	1,199,164		22,878	(1,159)	1,220,883
Total debt securities	$	10,374,587	90,995	(73,850)	10,391,732

The following table presents the amortized cost and fair value of available-for-sale and held-to-maturity debt securities by contractual maturity at March 31, 2022. Actual maturities may differ from expected or contractual maturities since some issuers have the right to prepay obligations with or without prepayment penalties.


	March 31, 2022
	Available-for-Sale			Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Fair Value	Amortized Cost	Fair Value
Due within one year	$	55,445	56,042	1,426	1,429
Due after one year through five years	907,525		867,786	399,508	384,761
Due after five years through ten years	187,949		189,242	569,111	546,644
Due after ten years	227,592		231,266	1,258,735	1,169,129
	1,378,511		1,344,336	2,228,780	2,101,963
Mortgage-backed securities 1	5,476,546		5,191,427	1,348,161	1,292,869
Total	$	6,855,057	6,535,763	3,576,941	3,394,832

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
(Dollars in thousands)	March 31, 2022		March 31, 2021
Available-for-sale
Proceeds from sales and calls of debt securities	$	53,120	54,336
Gross realized gains 1	693		369
Gross realized losses 1	(15)		(43)
Held-to-maturity
Proceeds from calls of debt securities	12,975		4,130
Gross realized gains 1	15		—
Gross realized losses 1	(247)		(42)

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.


	March 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	44	$	453,390	(25,657)	4,248	(337)	457,638	(25,994)
U.S. government sponsored enterprises	15	302,350		(16,707)	—	—	302,350	(16,707)
State and local governments	93	49,442		(2,040)	1,646	(150)	51,088	(2,190)
Corporate bonds	3	5,421		(83)	—	—	5,421	(83)
Residential mortgage-backed securities	354	3,164,385		(195,824)	738,114	(53,664)	3,902,499	(249,488)
Commercial mortgage-backed securities	105	757,925		(30,284)	128,637	(11,484)	886,562	(41,768)
Total available-for-sale	614	$	4,732,913	(270,595)	872,645	(65,635)	5,605,558	(336,230)


	December 31, 2021
	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	50	$	1,329,399	(9,344)	5,457	(252)	1,334,856	(9,596)
U.S. government sponsored enterprises	11	239,928		(996)	—	—	239,928	(996)
State and local governments	10	11,080		(83)	1,760	(40)	12,840	(123)
Corporate bonds	3	12,483		(17)	—	—	12,483	(17)
Residential mortgage-backed securities	151	5,335,632		(53,434)	53,045	(832)	5,388,677	(54,266)
Commercial mortgage-backed securities	38	302,784		(3,316)	126,798	(4,377)	429,582	(7,693)
Total available-for-sale	263	$	7,231,306	(67,190)	187,060	(5,501)	7,418,366	(72,691)

With respect to severity, the majority of available-for-sale debt securities with unrealized loss positions at March 31, 2022 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 March 31, 2022 have been determined to be investment grade.

The Company did not have any past due available-for-sale debt securities as of March 31, 2022 and December 31, 2021, respectively. Accrued interest receivable on available-for-sale debt securities totaled $16,758,000 and $18,788,000 at March 31, 2022, and December 31, 2021, 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 March 31, 2022, 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 March 31, 2022, 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 March 31, 2022. 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)	March 31, 2022		December 31, 2021
Municipal bonds held-to-maturity
S&P: AAA / Moody’s: Aaa	$	329,796	316,899
S&P: AA+, AA, AA- / Moody’s: Aa1, Aa2, Aa3	1,015,536		841,616
S&P: A+, A, A- / Moody’s: A1, A2, A3	38,617		39,078

Not rated by either entity	1,567		1,571

Total municipal bonds held-to-maturity	$	1,385,516	1,199,164

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 March 31, 2022 have been determined to be investment grade. Held-to-maturity debt securities issued and guaranteed by the U.S. Treasury, Fannie Mae, Freddie Mac, Government National Mortgage Association (“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 March 31, 2022 and December 31, 2021, the Company did not have any held-to-maturity debt securities past due. Accrued interest receivable on held-to-maturity debt securities totaled $16,150,000 and $8,737,000 at March 31, 2022 and December 31, 2021, 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 March 31, 2022 or December 31, 2021.