
	December 31, 2022
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Estimated Fair Value
Debt Securities Available for Sale
Obligations of U.S. government agencies	$	1,568,408	$	3	$	(195,642)	$	—	$	1,372,769
Obligations of states and political subdivisions	332,625		401		(39,821)		—		293,205
Corporate bonds	6,164		—		(413)		—		5,751
Asset backed securities	454,943		17		(15,193)		—		439,767
Non-agency collateralized mortgage obligations	380,847		—		(39,901)		—		340,946
Total debt securities available for sale	$	2,742,987	$	421	$	(290,970)	$	—	$	2,452,438
Debt Securities Held to Maturity
Obligations of U.S. government agencies	$	154,830	$	2	$	(11,013)	$	—	$	143,819
Obligations of states and political subdivisions	6,153		13		(47)		—		6,119
Total debt securities held to maturity	$	160,983	$	15	$	(11,060)	$	—	$	149,938

There were no proceeds from sale of investment securing during the three months ended September 30, 2023. Proceeds from the sale of investment securities totaled $24.2 million for the nine months ended September 30, 2023, resulting in gross realized losses of $0.2 million. There were no sales of investment securities during the three and nine months ended September 30, 2022. Investment securities with an aggregate carrying value of $585.0 million and $595.8 million at September 30, 2023 and December 31, 2022, respectively, were pledged as collateral for specific borrowings, lines of credit or local agency deposits.

The amortized cost and estimated fair value of debt securities at September 30, 2023 by contractual maturity are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. At September 30, 2023, obligations of U.S. government corporations and agencies with a cost basis totaling $1.4 billion consist almost entirely of residential real estate mortgage-backed securities whose contractual maturity, or principal repayment, will follow the repayment of the underlying mortgages. For purposes of the following table, the entire outstanding balance of these mortgage-backed securities issued by U.S. government corporations and agencies is categorized based on final maturity date. At September 30, 2023, the Company estimates the average remaining life of these mortgage-backed securities issued by U.S. government corporations and agencies to be approximately 6.77 years. Average remaining life is defined as the time span after which the principal balance has been reduced by half.


Debt Securities	Available for Sale				Held to Maturity
(in thousands)	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value

Due in one year	$	86,722	$	84,609	$	—	$	—
Due after one year through five years	62,069		58,068		6,302		6,015
Due after five years through ten years	398,920		377,030		80,279		71,376
Due after ten years	1,961,912		1,654,630		52,477		46,667
Totals	$	2,509,623	$	2,174,337	$	139,058	$	124,058

Gross unrealized losses on debt securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, were as follows:


September 30, 2023:	Less than 12 months				12 months or more				Total
(in thousands)	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Debt Securities Available for Sale
Obligations of U.S. government agencies	$	413	$	(14)	$	1,206,736	$	(235,852)	$	1,207,149	$	(235,866)
Obligations of states and political subdivisions	46,600		(2,674)		207,415		(45,972)		254,015		(48,646)
Corporate bonds	—		—		5,505		(665)		5,505		(665)
Asset backed securities	—		—		309,126		(5,730)		309,126		(5,730)
Non-agency collateralized mortgage obligations	44,591		(1,236)		288,671		(43,558)		333,262		(44,794)
Total debt securities available for sale	$	91,604	$	(3,924)	$	2,017,453	$	(331,777)	$	2,109,057	$	(335,701)
Debt Securities Held to Maturity
Obligations of U.S. government agencies	$	233	$	(2)	$	121,340	$	(14,822)	$	121,573	$	(14,824)
Obligations of states and political subdivisions	1,547		(59)		938		(117)		2,485		(176)
Total debt securities held to maturity	$	1,780	$	(61)	$	122,278	$	(14,939)	$	124,058	$	(15,000)


December 31, 2022:	Less than 12 months				12 months or more				Total
(in thousands)	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Debt Securities Available for Sale
Obligations of U.S. government agencies	$	605,615	$	(61,408)	$	766,612	$	(134,234)	$	1,372,227	$	(195,642)
Obligations of states and political subdivisions	219,532		(26,904)		43,282		(12,917)		262,814		(39,821)
Corporate bonds	5,751		(413)		—		—		5,751		(413)
Asset backed securities	231,703		(4,955)		205,329		(10,238)		437,032		(15,193)
Non-agency collateralized mortgage obligations	123,075		(3,421)		203,620		(36,480)		326,695		(39,901)
Total debt securities available for sale	$	1,185,676	(97,101)		$	1,218,843	$	(193,869)	$	2,404,519	$	(290,970)
Debt Securities Held to Maturity
Obligations of U.S. government agencies	$	143,577	$	(11,013)	$	—	$	—	$	143,577	$	(11,013)
Obligations of states and political subdivisions	4,530		(47)		—		—		4,530		(47)
Total debt securities held to maturity	$	148,107	$	(11,060)	$	—	$	—	$	148,107	$	(11,060)

Obligations of U.S. government agencies: The unrealized losses on investments in obligations of U.S. government agencies are caused by interest rate increases and illiquidity. The contractual cash flows of these securities are guaranteed by U.S. Government Sponsored Entities (principally Fannie Mae and Freddie Mac). It is expected that the securities would not be settled at a price less than the amortized cost of the investment. Because management believes the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, there is no impairment on these securities and there has been no allowance for credit losses recorded. At September 30, 2023, 263 debt securities representing obligations of U.S. government agencies had unrealized losses with aggregate depreciation of 15.87% from the Company’s amortized cost basis.

Obligations of states and political subdivisions: The unrealized losses on investments in obligations of states and political subdivisions were caused by increases in required yields by investors in these types of securities. It is expected that the securities would not be settled at a price less than the amortized cost of the investment. Because management believes the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, there is no impairment on these securities and there has been no allowance for credit losses recorded as of September 30, 2023. At September 30, 2023, 184 debt securities representing obligations of states and political subdivisions had unrealized losses with aggregate depreciation of 15.99% from the Company’s amortized cost basis.

Corporate bonds: The unrealized losses on investments in corporate bonds were caused by increases in required yields by investors in these types of securities. It is expected that the securities would not be settled at a price less than the amortized cost of the investment. Because management believes the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, there is no impairment on these securities and there has been no allowance for credit losses recorded as of September 30, 2023. At September 30, 2023, 6 debt securities representing corporate bonds had unrealized losses with aggregate depreciation of 10.78% from the Company’s amortized cost basis.

Asset backed securities: The unrealized losses on investments in asset backed securities were caused by increases in required yields by investors for these types of securities. At the time of purchase, each of these securities was rated AA or AAA and through September 30,

2023 has not experienced any deterioration in credit rating. At September 30, 2023, 40 asset backed securities had unrealized losses with aggregate depreciation of 1.82% from the Company’s amortized cost basis. The Company continues to monitor these securities for changes in credit rating or other indications of credit deterioration. Because management believes the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, there is no impairment on these securities and there has been no allowance for credit losses recorded as of September 30, 2023.

Non-agency collateralized mortgage obligations: The unrealized losses on investments in non-agency collateralized mortgage obligation securities were caused by increases in required yields by investors in these types of securities. It is expected that the securities would not be settled at a price less than the amortized cost of the investment. Because management believes the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, there is no impairment on these securities and there has been no allowance for credit losses as of and for the year ended September 30, 2023. At September 30, 2023, 24 non-agency collateralized mortgage obligation securities had unrealized losses with aggregate depreciation of 11.85% from the Company’s amortized cost basis.

The Company monitors credit quality of debt securities held-to-maturity through the use of credit rating. The Company monitors the credit rating on a monthly basis. The following table summarizes the amortized cost of debt securities held-to-maturity at the dates indicated, aggregated by credit quality indicator:


	September 30, 2023				December 31, 2022
(in thousands)	AAA/AA/A		BBB/BB/B		AAA/AA/A		BBB/BB/B
Obligations of U.S. government agencies	$	136,398	$	—	$	154,830	$	—
Obligations of states and political subdivisions	2,660		—		6,153		—
Total debt securities held to maturity	$	139,058	$	—	$	160,983	$	—