At March 31, 2022, the Company had $2.07 billion and $422.0 million in available for sale debt securities and held to maturity debt securities, respectively. Many factors, including lack of liquidity in the secondary market for certain securities, variations in pricing information, regulatory actions, changes in the business environment or any changes in the competitive marketplace could have an adverse effect on the Company’s investment portfolio. The total number of available for sale and held to maturity debt securities in an unrealized loss position at March 31, 2022 totaled 489, compared with 166 at December 31, 2021. The increase in the number of securities in an unrealized loss position at March 31, 2022 was due to higher current market interest rates compared to rates at December 31, 2021.

Management measures expected credit losses on held to maturity debt securities on a collective basis by security type. Management classifies the held to maturity debt securities portfolio into the following security types:

All of the agency obligations held by the Company are issued by U.S. government 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. The majority of the state and municipal, and corporate obligations carry no lower than A ratings from the rating agencies at March 31, 2022 and the Company had one security rated BBB by Moody’s Investors Service.

The following tables present the amortized cost, gross unrealized gains, gross unrealized losses and the fair value for available for sale debt securities at March 31, 2022 and December 31, 2021 (in thousands):


	March 31, 2022
	Amortized cost		Gross unrealized gains	Gross unrealized losses	Fair value

U.S. Treasury obligations	$	274,876	—	(14,711)	260,165

Mortgage-backed securities	1,767,392		1,132	(98,060)	1,670,464
Asset-backed securities	43,895		1,139	(98)	44,936
State and municipal obligations	68,453		31	(4,638)	63,846
Corporate obligations	34,088		239	(1,401)	32,926

	$	2,188,704	2,541	(118,908)	2,072,337


	December 31, 2021
	Amortized cost		Gross unrealized gains	Gross unrealized losses	Fair value

U.S. Treasury obligations	$	196,897	298	(866)	196,329

Mortgage-backed securities	1,711,312		14,082	(16,563)	1,708,831
Asset-backed securities	45,115		1,687	(5)	46,797
State and municipal obligations	68,702		1,127	(122)	69,707
Corporate obligations	36,109		425	(347)	36,187

	$	2,058,135	17,619	(17,903)	2,057,851

The amortized cost and fair value of available for sale debt securities at March 31, 2022, by contractual maturity, are shown below (in thousands). Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer.


	March 31, 2022
	Amortized cost		Fair value
Due in one year or less	$	997	1,005
Due after one year through five years	137,234		130,466
Due after five years through ten years	174,136		164,946
Due after ten years	65,050		60,520
	$	377,417	356,937

Investments which pay principal on a periodic basis totaling $1.81 billion at amortized cost and $1.72 billion at fair value are excluded from the table above, as their expected lives are likely to be shorter than the contractual maturity date due to principal prepayments.

For the three months ended March 31, 2022, no securities were sold or called from the available for sale debt securities portfolio. For the three months ended March 31, 2021, proceeds from calls on securities in the available for sale debt securities portfolio totaled $9.4 million, with gains of $230,000 and no loss recognized.

The following tables present the fair values and gross unrealized losses for available for sale debt securities in an unrealized loss position at March 31, 2022 and December 31, 2021 (in thousands):


	March 31, 2022
	Less than 12 months			12 months or longer		Total
	Fair value		Gross unrealized losses	Fair value	Gross unrealized losses	Fair value	Gross unrealized losses

U.S. Treasury obligations	$	260,165	(14,711)	—	—	260,165	(14,711)
Mortgage-backed securities	1,352,508		(84,395)	155,913	(13,665)	1,508,422	(98,060)
Asset-backed securities	1,810		(98)	—	—	1,810	(98)
State and municipal obligations	60,024		(4,638)	—	—	60,024	(4,638)
Corporate obligations	14,270		(730)	6,124	(671)	20,394	(1,401)
	$	1,688,777	(104,572)	162,037	(14,336)	1,850,815	(118,908)


	December 31, 2021
	Less than 12 months			12 months or longer		Total
	Fair value		Gross unrealized losses	Fair value	Gross unrealized losses	Fair value	Gross unrealized losses
U.S. Treasury obligations	$	98,621	(866)	—	—	98,621	(866)

Mortgage-backed securities	1,147,403		(15,176)	33,850	(1,387)	1,181,253	(16,563)
Asset-backed securities	1,930		(5)	—	—	1,930	(5)
State and municipal obligations	10,732		(122)	—	—	10,732	(122)
Corporate obligations	18,474		(347)	—	—	18,474	(347)
	$	1,277,160	(16,516)	33,850	(1,387)	1,311,010	(17,903)

The number of available for sale debt securities in an unrealized loss position at March 31, 2022 totaled 309, compared with 113 at December 31, 2021. The increase in the number of securities in an unrealized loss position at March 31, 2022 was due to higher current market interest rates compared to rates at December 31, 2021. At March 31, 2022, there were three private label mortgage-backed securities in an unrealized loss position, with an amortized cost of $3.4 million and an unrealized loss of $212,000. These private-label mortgage-backed securities were investment grade at March 31, 2022.

The following tables present the amortized cost, gross unrealized gains, gross unrealized losses and the estimated fair value for held to maturity debt securities at March 31, 2022 and December 31, 2021 (in thousands):


	March 31, 2022
	Amortized cost		Gross unrealized gains	Gross unrealized losses	Fair value
U.S. Treasury obligations	$	1,430	—	—	1,430
Agency obligations	9,997		—	(622)	9,375
Mortgage-backed securities	13		—	—	13
State and municipal obligations	400,629		3,411	(6,625)	397,415
Corporate obligations	9,923		1	(493)	9,431
	$	421,992	3,412	(7,740)	417,664


	December 31, 2021
	Amortized cost		Gross unrealized gains	Gross unrealized losses	Fair value
Agency obligations	$	9,996	—	(175)	9,821
Mortgage-backed securities	21		—	—	21
State and municipal obligations	415,724		14,463	(635)	429,552
Corporate obligations	10,448		19	(152)	10,315
	$	436,189	14,482	(962)	449,709

The Company generally purchases securities for long-term investment purposes, and differences between amortized cost and fair value may fluctuate during the investment period. There were no sales of securities from the held to maturity debt securities portfolio for the three months ended March 31, 2022 and 2021. For the three months ended March 31, 2022, proceeds from calls on securities in the held to maturity debt securities portfolio totaled $15.8 million with gross gains of $16,000 and no gross losses. For the three months ended March 31, 2021, proceeds from calls on securities in the held to maturity debt securities portfolio totaled $6.8 million with gross losses of $33,000 and no gross gains.

The amortized cost and fair value of investment securities in the held to maturity debt securities portfolio at March 31, 2022 by contractual maturity are shown below (in thousands). Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer.


	March 31, 2022
	Amortized cost		Fair value
Due in one year or less	$	17,286	17,338
Due after one year through five years	153,590		152,915
Due after five years through ten years	194,905		194,739
Due after ten years	56,198		52,659
	$	421,979	417,651

Mortgage-backed securities totaling $13,000 at amortized cost and $13,000 at fair value are excluded from the table above, as their expected lives are likely to be shorter than the contractual maturity date due to principal prepayments. Additionally, the allowance for credit losses totaling $34,000 is excluded from the table above.

The following tables present the fair values and gross unrealized losses for held to maturity debt securities in an unrealized loss position at March 31, 2022 and December 31, 2021 (in thousands):


	March 31, 2022 Unrealized Losses
	Less than 12 months			12 months or longer		Total
	Fair value		Gross unrealized losses	Fair value	Gross unrealized losses	Fair value	Gross unrealized losses
Agency obligations	$	9,374	(622)	—	—	9,374	(622)
State and municipal obligations	90,209		(5,480)	8,482	(1,145)	98,691	(6,625)
Corporate obligations	8,105		(493)	—	—	8,105	(493)
	$	107,688	(6,595)	8,482	(1,145)	116,170	(7,740)


	December 31, 2021 Unrealized Losses
	Less than 12 months			12 months or longer		Total
	Fair value		Gross unrealized losses	Fair value	Gross unrealized losses	Fair value	Gross unrealized losses
Agency obligations	$	9,821	(175)	—	—	9,821	(175)
State and municipal obligations	27,350		(471)	5,022	(164)	32,372	(635)
Corporate obligations	7,649		(152)	—	—	7,649	(152)
	$	44,820	(798)	5,022	(164)	49,842	(962)

The number of held to maturity debt securities in an unrealized loss position at March 31, 2022 totaled 180, compared with 53 at December 31, 2021. The increase in the number of securities in an unrealized loss position at March 31, 2022, was due to higher current market interest rates compared to rates at December 31, 2021.

Credit Quality Indicators. The following table provides the amortized cost of held to maturity debt securities by credit rating as of March 31, 2022 (in thousands):


	March 31, 2022
Total Portfolio	AAA		AA	A	BBB	Not Rated	Total
Treasury Obligations	$	1,430	—	—	—	—	1,430
Agency obligations	9,997		—	—	—	—	9,997
Mortgage-backed securities	13		—	—	—	—	13
State and municipal obligations	53,191		305,861	39,664	945	968	400,629
Corporate obligations	509		2,124	7,265	—	25	9,923
	$	65,140	307,985	46,929	945	993	421,992

	December 31, 2021
Total Portfolio	AAA		AA	A	BBB	Not Rated	Total
Agency obligations	$	9,996	—	—	—	—	9,996
Mortgage-backed securities	21		—	—	—	—	21
State and municipal obligations	54,583		314,396	44,392	945	1,408	415,724
Corporate obligations	510		2,634	7,279	—	25	10,448
	$	65,110	317,030	51,671	945	1,433	436,189

Credit quality indicators are metrics that provide information regarding the relative credit risk of debt securities. At March 31, 2022, the held to maturity debt securities portfolio was comprised of 15% rated AAA, 73% rated AA, 11% rated A, and less than 1% either below an A rating or not rated by Moody’s Investors Service or Standard and Poor’s. Securities not explicitly rated, such as U.S. Government mortgage-backed securities, were grouped where possible under the credit rating of the issuer of the security.