Debt Securities

3 Months Ended

Mar. 31, 2025

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, 2025
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	1,426,351	$	4,536	$	(57,854)	$	1,373,033
Obligations of states and political subdivisions	1,051,171		2,735		(33,064)		1,020,842
Mortgage-backed securities and collateralized mortgage obligations	6,204,692		21,727		(391,489)		5,834,930
Total available for sale securities	$	8,682,214	$	28,998	$	(482,407)	$	8,228,805
Held to maturity:
Mortgage-backed securities and collateralized mortgage obligations	$	2,057	$	588	$	—	$	2,645
Total held to maturity securities	$	2,057	$	588	$	—	$	2,645


	December 31, 2024
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	1,495,542	$	1,092	$	(73,847)	$	1,422,787
Obligations of states and political subdivisions	1,055,535		2,779		(32,261)		1,026,053
Mortgage-backed securities and collateralized mortgage obligations	6,307,252		3,937		(485,414)		5,825,775
Total available for sale securities	$	8,858,329	$	7,808	$	(591,522)	$	8,274,615
Held to maturity:
Mortgage-backed securities and collateralized mortgage obligations	$	2,101	$	602	$	—	$	2,703
Total held to maturity securities	$	2,101	$	602	$	—	$	2,703

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 $31.9 million and $32.9 million as of March 31, 2025 and December 31, 2024, 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, 2025
	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	$	99,739	$	(1,010)	$	762,609	$	(56,844)	$	862,348	$	(57,854)
Obligations of states and political subdivisions	485,272		(9,118)		269,731		(23,946)		755,003		(33,064)
Mortgage-backed securities and collateralized mortgage obligations	1,795,282		(25,616)		1,837,923		(365,873)		3,633,205		(391,489)
Total temporarily impaired securities	$	2,380,293	$	(35,744)	$	2,870,263	$	(446,663)	$	5,250,556	$	(482,407)


	December 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	$	185,042	$	(2,770)	$	794,521	$	(71,077)	$	979,563	$	(73,847)
Obligations of states and political subdivisions	539,440		(8,036)		224,973		(24,225)		764,413		(32,261)
Mortgage-backed securities and collateralized mortgage obligations	3,398,609		(78,817)		1,830,720		(406,597)		5,229,329		(485,414)

Total temporarily impaired securities	$	4,123,091	$	(89,623)	$	2,850,214	$	(501,899)	$	6,973,305	$	(591,522)

The number of individual debt securities in an unrealized loss position in the tables above decreased to 1,024 as of March 31, 2025, as compared to 1,210 at December 31, 2024. 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, 2025.

The following table presents the contractual maturities of debt securities as of March 31, 2025:


	Available For Sale				Held To Maturity
(in thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	263,071	$	263,740	$	—	$	—
Due after one year through five years	2,752,447		2,720,313		2		2
Due after five years through ten years	1,522,998		1,467,666		1		554
Due after ten years	4,143,698		3,777,086		2,054		2,089
Total debt securities	$	8,682,214	$	8,228,805	$	2,057	$	2,645

At March 31, 2025 and December 31, 2024, investment securities with a fair value of $6.7 billion and $6.2 billion, respectively, were pledged to secure borrowing capacity, public deposits, repurchase agreements, and for other purposes as required or permitted by law.