Securities (Tables)

3 Months Ended

Mar. 31, 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):

	March 31, 2025
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	216,650	$	3	$	(2,979	)	$	213,674
Obligations of states and political subdivisions		1,569,885		239		(160,637	)		1,409,487
Residential mortgage-backed securities		2,727,421		2,126		(324,666	)		2,404,881
Commercial mortgage-backed securities		627,318		4,040		(5,697	)		625,661
Corporate bonds and other		111,825		64		(5,161	)		106,728
Total securities available-for-sale	$	5,253,099	$	6,472	$	(499,140	)	$	4,760,431

	March 31, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	445,399	$	—	$	(13,231	)	$	432,168
Obligations of states and political subdivisions		1,592,523		570		(139,058	)		1,454,035
Residential mortgage-backed securities		2,685,896		72		(386,691	)		2,299,277
Commercial mortgage-backed securities		381,198		52		(12,344	)		368,906
Corporate bonds and other		112,501		—		(8,361	)		104,140
Total securities available-for-sale	$	5,217,517	$	694	$	(559,685	)	$	4,658,526

	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 March 31, 2025, by contractual and expected maturity, are shown below (dollars in thousands):

	Carrying		Estimated
	Value		Fair Value
Due within one year	$	279,646	$	276,226
Due after one year through five years		1,868,240		1,754,031
Due after five years through ten years		1,795,546		1,608,902
Due after ten years		1,309,667		1,121,272
Total	$	5,253,099	$	4,760,431

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

The following tables disclose as of March 31, 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
March 31, 2025	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	—	$	—		$	211,193	$	(2,979	)	$	211,193	$	(2,979	)
Obligations of states and political subdivisions		72,501		(2,111	)		1,329,121		(158,526	)		1,401,622		(160,637	)
Residential mortgage-backed securities		167,666		(1,950	)		2,059,869		(322,716	)		2,227,535		(324,666	)
Commercial mortgage-backed securities		16,992		(179	)		188,744		(5,518	)		205,736		(5,697	)
Corporate bonds and other		9,908		(14	)		91,832		(5,147	)		101,740		(5,161	)
Total	$	267,067	$	(4,254	)	$	3,880,759	$	(494,886	)	$	4,147,826	$	(499,140	)

	Less than 12 Months					12 Months or Longer					Total
March 31, 2024	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	2,438	$	(16	)	$	429,730	$	(13,215	)	$	432,168	$	(13,231	)
Obligations of states and political subdivisions		33,073		(114	)		1,398,108		(138,944	)		1,431,181		(139,058	)
Residential mortgage-backed securities		22,586		(299	)		2,261,311		(386,392	)		2,283,897		(386,691	)
Commercial mortgage-backed securities		64,721		(507	)		275,924		(11,837	)		340,645		(12,344	)
Corporate bonds and other		—		—			104,140		(8,361	)		104,140		(8,361	)
Total	$	122,818	$	(936	)	$	4,469,213	$	(558,749	)	$	4,592,031	$	(559,685	)

	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	)