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Securities (Tables)

9 Months Ended

Sep. 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):


		September 30, 2025
						Gross				Gross
		Amortized				Unrealized				Unrealized				Estimated
		Cost Basis				Holding Gains				Holding Losses				Fair Value
Securities available-for-sale:
U.S. Treasury securities		$	102,865			$	2			$	(897	)		$	101,970
Obligations of states and political subdivisions			1,859,132				8,751				(133,972	)			1,733,911
Residential mortgage-backed securities			2,737,201				5,622				(272,025	)			2,470,798
Commercial mortgage-backed securities			849,026				8,580				(3,418	)			854,188
Corporate bonds and other			103,544				20				(3,618	)			99,946
Total securities available-for-sale		$	5,651,768			$	22,975			$	(413,930	)		$	5,260,813


		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


		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 September 30, 2025, by contractual and expected maturity, are shown below (dollars in thousands):


		Carrying				Estimated
		Value				Fair Value
Due within one year		$	225,746			$	223,945
Due after one year through five years			2,493,891				2,383,120
Due after five years through ten years			2,145,923				1,966,228
Due after ten years			786,208				687,520
Total		$	5,651,768			$	5,260,813

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

The following tables disclose as of September 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
September 30, 2025		Fair Value				Unrealized Loss				Fair Value				Unrealized Loss				Fair Value				Unrealized Loss
U.S. Treasury securities		$	1,000			$	—			$	99,476			$	(897	)		$	100,476			$	(897	)
Obligations of states and political subdivisions			21,278				(854	)			1,344,598				(133,118	)			1,365,876				(133,972	)
Residential mortgage-backed securities			125,497				(450	)			2,042,826				(271,575	)			2,168,323				(272,025	)
Commercial mortgage-backed securities			66,851				(74	)			166,330				(3,344	)			233,181				(3,418	)
Corporate bonds and other			—				—				82,982				(3,618	)			82,982				(3,618	)
Total		$	214,626			$	(1,378	)		$	3,736,212			$	(412,552	)		$	3,950,838			$	(413,930	)


		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
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	)