Securities

9 Months Ended

Sep. 30, 2024

Cash and Cash Equivalents [Abstract]

Securities

Note 2 - Securities

Debt securities have been classified in the consolidated balance sheets according to management’s intent. The amortized cost, related gross unrealized gains and losses, allowance for credit losses and the fair value of available-for-sale securities are as follows (dollars in thousands):

	September 30, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	298,671	$	14	$	(5,671	)	$	293,014
Obligations of states and political subdivisions		1,586,300		699		(115,516	)		1,471,483
Residential mortgage-backed securities		2,712,305		1,655		(290,030	)		2,423,930
Commercial mortgage-backed securities		320,685		1,946		(5,795	)		316,836
Corporate bonds and other		112,163		59		(5,186	)		107,036
Total securities available-for-sale	$	5,030,124	$	4,373	$	(422,198	)	$	4,612,299

	September 30, 2023
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	507,549	$	—	$	(22,102	)	$	485,447
Obligations of states and political subdivisions		1,726,947		120		(263,313	)		1,463,754
Residential mortgage-backed securities		2,792,813		—		(495,578	)		2,297,235
Commercial mortgage-backed securities		323,539		—		(18,191	)		305,348
Corporate bonds and other		112,338		—		(11,585	)		100,753
Total securities available-for-sale	$	5,463,186	$	120	$	(810,769	)	$	4,652,537

	December 31, 2023
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	496,975	$	4	$	(14,745	)	$	482,234
Obligations of states and political subdivisions		1,621,405		934		(125,182	)		1,497,157
Residential mortgage-backed securities		2,716,968		7		(352,883	)		2,364,092
Commercial mortgage-backed securities		295,663		—		(11,339	)		284,324
Corporate bonds and other		112,670		—		(7,715	)		104,955
Total securities available-for-sale	$	5,243,681	$	945	$	(511,864	)	$	4,732,762

The Company did not hold any securities classified as held-to-maturity at September 30, 2024, September 30, 2023, or December 31, 2023.

The Company invests in mortgage-backed securities that have expected maturities that differ from their contractual maturities. These differences arise because borrowers may have the right to call or prepay obligations with or without a prepayment penalty. These securities include collateralized mortgage obligations (CMOs) and other asset backed securities. The expected maturities of these securities at September 30, 2024 and 2023, and December 31, 2023, were computed by using scheduled amortization of balances and historical prepayment rates.

The carrying value and estimated fair value of available-for-sale securities at September 30, 2024, by contractual and expected maturity, are shown below (dollars in thousands):

	Carrying		Estimated
	Value		Fair Value
Due within one year	$	281,764	$	278,517
Due after one year through five years		1,758,382		1,662,649
Due after five years through ten years		2,167,043		1,955,247
Due after ten years		822,935		715,886
Total	$	5,030,124	$	4,612,299

The following tables disclose as of September 30, 2024 and 2023, and December 31, 2023, the Company’s investment securities that have been in a continuous unrealized-loss position for less than 12 months and for 12 or more months (dollars in thousands):

	Less than 12 Months				12 Months or Longer				Total
September 30, 2024	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	—	$	—	$	290,535	$	5,671	$	290,535	$	5,671
Obligations of states and political subdivisions		6,899		43		1,395,597		115,473	$	1,402,496	$	115,516
Residential mortgage-backed securities		124,439		335		2,205,425		289,695	$	2,329,864	$	290,030
Commercial mortgage-backed securities		7,118		32		209,632		5,763	$	216,750	$	5,795
Corporate bonds and other		—		—		97,183		5,186	$	97,183	$	5,186
Total	$	138,456	$	410	$	4,198,372	$	421,788	$	4,336,828	$	422,198

	Less than 12 Months				12 Months or Longer				Total
September 30, 2023	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	4,867	$	49	$	480,580	$	22,053	$	485,447	$	22,102
Obligations of states and political subdivisions		53,029		2,568		1,402,097		260,745		1,455,126		263,313
Residential mortgage-backed securities		3,123		106		2,294,112		495,472		2,297,235		495,578
Commercial mortgage-backed securities		1,274		87		304,074		18,104		305,348		18,191
Corporate bonds and other		—		—		100,753		11,585		100,753		11,585
Total	$	62,293	$	2,810	$	4,581,616	$	807,959	$	4,643,909	$	810,769

	Less than 12 Months				12 Months or Longer				Total
December 31, 2023	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	3,477	$	7	$	477,306	$	14,738	$	480,783	$	14,745
Obligations of states and political subdivisions		11,855		34		1,427,975		125,148		1,439,830		125,182
Residential mortgage-backed securities		1,631		1		2,361,089		352,882		2,362,720		352,883
Commercial mortgage-backed securities		—		—		284,324		11,339		284,324		11,339
Corporate bonds and other		—		—		104,955		7,715		104,955		7,715
Total	$	16,963	$	42	$	4,655,649	$	511,822	$	4,672,612	$	511,864