Investment Securities

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

The following tables present the amortized cost, unrealized gains, unrealized losses, and approximate fair values of debt securities as of the dates presented:


	March 31, 2024
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	1,552,240	$	1,132	$	(85,979)	$	1,467,393
Obligations of states and political subdivisions	1,068,290		8,788		(25,149)		1,051,929
Mortgage-backed securities and collateralized mortgage obligations	6,551,596		2,386		(456,759)		6,097,223
Total available for sale securities	$	9,172,126	$	12,306	$	(567,887)	$	8,616,545
Held to maturity:
Mortgage-backed securities and collateralized mortgage obligations	$	2,247	$	692	$	—	$	2,939
Total held to maturity securities	$	2,247	$	692	$	—	$	2,939


	December 31, 2023
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	1,551,074	$	6,192	$	(78,874)	$	1,478,392
Obligations of states and political subdivisions	1,073,264		20,451		(21,610)		1,072,105
Mortgage-backed securities and collateralized mortgage obligations	6,638,439		28,558		(387,624)		6,279,373
Total available for sale securities	$	9,262,777	$	55,201	$	(488,108)	$	8,829,870
Held to maturity:
Mortgage-backed securities and collateralized mortgage obligations	$	2,300	$	725	$	—	$	3,025
Total held to maturity securities	$	2,300	$	725	$	—	$	3,025

The Company elected to exclude accrued interest receivable from the amortized cost basis of debt securities disclosed throughout this note. Interest accrued on investment securities totaled $33.1 million and $34.1 million as of March 31, 2024 and December 31, 2023, respectively, and is included in other assets on the Condensed Consolidated Balance Sheets.

The following tables present debt securities that were in an unrealized loss position as of the dates presented, based on the length of time individual securities have been in an unrealized loss position.


	March 31, 2024
	Less than 12 Months				12 Months or Longer				Total
(in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Available for sale:
U.S. Treasury and agencies	$	338,230	$	(3,305)	$	816,265	$	(82,674)	$	1,154,495	$	(85,979)
Obligations of states and political subdivisions	297,204		(2,464)		182,355		(22,685)		479,559		(25,149)
Mortgage-backed securities and collateralized mortgage obligations	3,860,007		(51,572)		1,756,986		(405,187)		5,616,993		(456,759)
Total temporarily impaired securities	$	4,495,441	$	(57,341)	$	2,755,606	$	(510,546)	$	7,251,047	$	(567,887)


	December 31, 2023
	Less than 12 Months				12 Months or Longer				Total
(in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Available for sale:
U.S. Treasury and agencies	$	99,898	$	(1,074)	$	822,245	$	(77,800)	$	922,143	$	(78,874)
Obligations of states and political subdivisions	103,256		(580)		169,231		(21,030)		272,487		(21,610)
Mortgage-backed securities and collateralized mortgage obligations	1,089,640		(10,355)		1,817,768		(377,269)		2,907,408		(387,624)

Total temporarily impaired securities	$	1,292,794	$	(12,009)	$	2,809,244	$	(476,099)	$	4,102,038	$	(488,108)

The number of individual debt securities in an unrealized loss position in the tables above increased to 1,085 as of March 31, 2024, as compared to 600 at December 31, 2023. These unrealized losses on the debt securities held by the Company were caused by changes in market interest rates or the widening of market spreads subsequent to the initial purchase of these securities and are not due to the underlying credit of the issuers. Management monitors the published credit ratings of the issuers of the debt securities for material rating or outlook changes. As the decline in fair value of the debt securities is attributable to changes in interest rates or widening market spreads and not credit quality, these investments do not have an ACL as of March 31, 2024.

The following table presents the contractual maturities of debt securities as of March 31, 2024:


	Available For Sale				Held To Maturity
(in thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	141,688	$	139,856	$	—	$	—
Due after one year through five years	2,259,829		2,213,929		2		2
Due after five years through ten years	2,187,571		2,103,386		3		64
Due after ten years	4,583,038		4,159,374		2,242		2,873
Total debt securities	$	9,172,126	$	8,616,545	$	2,247	$	2,939

The following table presents, as of March 31, 2024, investment securities which were pledged to secure borrowings, public deposits, and repurchase agreements as permitted or required by law:


(in thousands)	Amortized Cost		Fair Value

To state and local governments to secure public deposits	$	1,800,912	$	1,638,230
To secure repurchase agreements	326,111		297,673
Other securities pledged	3,407,623		3,139,037
Total pledged securities	$	5,534,646	$	5,074,940