Securities (Tables)

6 Months Ended

Jun. 30, 2025

Cash and Cash Equivalents [Abstract]

Summary of Available-for-Sale Securities

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):

	June 30, 2025
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	155,710	$	1	$	(1,876	)	$	153,835
Obligations of states and political subdivisions		1,694,153		743		(173,532	)		1,521,364
Residential mortgage-backed securities		2,708,501		3,521		(300,148	)		2,411,874
Commercial mortgage-backed securities		704,579		6,875		(4,436	)		707,018
Corporate bonds and other		96,723		10		(4,276	)		92,457
Total securities available-for-sale	$	5,359,666	$	11,150	$	(484,268	)	$	4,886,548

	June 30, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	352,682	$	—	$	(10,706	)	$	341,976
Obligations of states and political subdivisions		1,584,389		420		(139,436	)		1,445,373
Residential mortgage-backed securities		2,705,508		71		(389,494	)		2,316,085
Commercial mortgage-backed securities		362,004		—		(11,982	)		350,022
Corporate bonds and other		127,868		—		(8,300	)		119,568
Total securities available-for-sale	$	5,132,451	$	491	$	(559,918	)	$	4,573,024

	December 31, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	278,155	$	2	$	(4,595	)	$	273,562
Obligations of states and political subdivisions		1,578,749		338		(138,842	)		1,440,245
Residential mortgage-backed securities		2,729,096		184		(378,746	)		2,350,534
Commercial mortgage-backed securities		457,311		99		(9,658	)		447,752
Corporate bonds and other		111,994		50		(6,378	)		105,666
Total securities available-for-sale	$	5,155,305	$	673	$	(538,219	)	$	4,617,759

Carrying Value and Estimated Fair Value of Available-for-Sale Securities

The carrying value and estimated fair value of available-for-sale securities at June 30, 2025, by contractual and expected maturity, are shown below (dollars in thousands):

	Carrying		Estimated
	Value		Fair Value
Due within one year	$	282,480	$	279,764
Due after one year through five years		2,103,481		1,986,766
Due after five years through ten years		1,631,680		1,477,793
Due after ten years		1,342,025		1,142,225
Total	$	5,359,666	$	4,886,548

Continuous Unrealized-Loss Position of Available-for-Sale Securities

The following tables disclose as of June 30, 2025 and 2024, and December 31, 2024, 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
June 30, 2025	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	1,497	$	—		$	151,350	$	(1,876	)	$	152,847	$	(1,876	)
Obligations of states and political subdivisions		74,621		(2,300	)		1,308,960		(171,232	)		1,383,581		(173,532	)
Residential mortgage-backed securities		166,062		(1,315	)		2,011,749		(298,833	)		2,177,811		(300,148	)
Commercial mortgage-backed securities		7,194		(130	)		181,352		(4,306	)		188,546		(4,436	)
Corporate bonds and other		—		—			87,513		(4,276	)		87,513		(4,276	)
Total	$	249,374	$	(3,745	)	$	3,740,924	$	(480,523	)	$	3,990,298	$	(484,268	)

	Less than 12 Months					12 Months or Longer					Total
June 30, 2024	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	1,448	$	(12	)	$	340,528	$	(10,694	)	$	341,976	$	(10,706	)
Obligations of states and political subdivisions		32,423		(320	)		1,391,496		(139,117	)		1,423,919		(139,437	)
Residential mortgage-backed securities		80,096		(462	)		2,183,346		(389,031	)		2,263,442		(389,493	)
Commercial mortgage-backed securities		92,487		(928	)		257,535		(11,054	)		350,022		(11,982	)
Corporate bonds and other		—		—			104,031		(8,300	)		104,031		(8,300	)
Total	$	206,454	$	(1,722	)	$	4,276,936	$	(558,196	)	$	4,483,390	$	(559,918	)

	Less than 12 Months					12 Months or Longer					Total
December 31, 2024	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	—	$	—		$	271,088	$	(4,595	)	$	271,088	$	(4,595	)
Obligations of states and political subdivisions		56,777		(1,224	)		1,361,628		(137,618	)		1,418,405		(138,842	)
Residential mortgage-backed securities		198,385		(4,990	)		2,048,727		(373,756	)		2,247,112		(378,746	)
Commercial mortgage-backed securities		196,640		(2,249	)		190,189		(7,409	)		386,829		(9,658	)
Corporate bonds and other		4,871		(44	)		95,840		(6,334	)		100,711		(6,378	)
Total	$	456,673	$	(8,507	)	$	3,967,472	$	(529,712	)	$	4,424,145	$	(538,219	)