Securities (Tables)

3 Months Ended

Mar. 31, 2024

Securities Available for Sale

This table provides detailed information about securities available for sale at March 31, 2024 and December 31, 2023 (in thousands):

March 31, 2024	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	809,561	$	155	$	(7,216	)	$	802,500
U.S. Agencies		161,766		4		(2,748	)		159,022
Mortgage-backed		4,213,875		463		(540,155	)		3,674,183
State and political subdivisions		1,323,080		563		(89,723	)		1,233,920
Corporates		357,878		—		(27,841	)		330,037
Collateralized loan obligations		341,171		945		(387	)		341,729
Total	$	7,207,331	$	2,130	$	(668,070	)	$	6,541,391

December 31, 2023	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	1,308,689	$	254	$	(10,201	)	$	1,298,742
U.S. Agencies		162,406		252		(2,937	)		159,721
Mortgage-backed		4,128,576		949		(508,740	)		3,620,785
State and political subdivisions		1,359,744		2,218		(74,987	)		1,286,975
Corporates		382,069		—		(30,794	)		351,275
Collateralized loan obligations		351,376		811		(1,072	)		351,115
Total	$	7,692,860	$	4,484	$	(628,731	)	$	7,068,613

Gross Unrealized Losses and Fair Value of Investment Securities Available for Sale

The following table shows the Company’s available-for-sale investments’ gross unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at March 31, 2024 and December 31, 2023 (in thousands):

	Less than 12 months							12 months or more							Total
March 31, 2024	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury		46	$	296,702	$	(1,282	)		30	$	417,698	$	(5,934	)		76	$	714,400	$	(7,216	)
U.S. Agencies		10		61,842		(262	)		7		87,124		(2,486	)		17		148,966		(2,748	)
Mortgage-backed		35		189,438		(1,471	)		848		3,387,309		(538,684	)		883		3,576,747		(540,155	)
State and political subdivisions		285		193,120		(10,338	)		1,639		951,910		(79,385	)		1,924		1,145,030		(89,723	)
Corporates		—		—		—			253		327,473		(27,841	)		253		327,473		(27,841	)
Collateralized loan obligations		6		38,585		(47	)		22		156,183		(340	)		28		194,768		(387	)
Total		382	$	779,687	$	(13,400	)		2,799	$	5,327,697	$	(654,670	)		3,181	$	6,107,384	$	(668,070	)

	Less than 12 months							12 months or more							Total
December 31, 2023	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury		8	$	509,946	$	(267	)		63	$	745,573	$	(9,934	)		71	$	1,255,519	$	(10,201	)
U.S. Agencies		—		—		—			16		116,324		(2,937	)		16		116,324		(2,937	)
Mortgage-backed		14		19,154		(476	)		852		3,526,296		(508,264	)		866		3,545,450		(508,740	)
State and political subdivisions		388		200,835		(9,202	)		1,476		890,545		(65,785	)		1,864		1,091,380		(74,987	)
Corporates		—		—		—			267		351,275		(30,794	)		267		351,275		(30,794	)
Collateralized loan obligations		1		4,246		(4	)		32		210,872		(1,068	)		33		215,118		(1,072	)
Total		411	$	734,181	$	(9,949	)		2,706	$	5,840,885	$	(618,782	)		3,117	$	6,575,066	$	(628,731	)

Gross Unrealized Losses and Fair Value of Investment Securities Held to Maturity

The following table shows the Company’s held-to-maturity investments’ gross unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at March 31, 2024 and December 31, 2023, respectively (in thousands):

	Less than 12 months							12 months or more							Total
March 31, 2024	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
U.S. Agencies		—	$	—	$	—			11	$	120,579	$	(2,661	)		11	$	120,579	$	(2,661	)
Mortgage-backed		6		3,618		(56	)		263		2,282,995		(404,464	)		269		2,286,613		(404,520	)
State and political subdivisions		70		252,000		(11,364	)		1,426		1,900,331		(198,711	)		1,496		2,152,331		(210,075	)
Total		76	$	255,618	$	(11,420	)		1,700	$	4,303,905	$	(605,836	)		1,776	$	4,559,523	$	(617,256	)

	Less than 12 months							12 months or more							Total
December 31, 2023	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
U.S. Agency		—	$	—	$	—			11	$	120,524	$	(2,686	)		11	$	120,524	$	(2,686	)
Mortgage-backed		2		1,469		(14	)		263		2,377,922		(356,643	)		265		2,379,391		(356,657	)
State and political subdivisions		146		570,950		(22,557	)		1,343		1,612,442		(147,640	)		1,489		2,183,392		(170,197	)
Total		148	$	572,419	$	(22,571	)		1,617	$	4,110,888	$	(506,969	)		1,765	$	4,683,307	$	(529,540	)

Schedule of Amortized Cost Basis by Credit Rating of Held to Maturity Investment

The following tables show the amortized cost basis by credit rating of the Company’s held-to-maturity State and political subdivisions bond investments at March 31, 2024 and December 31, 2023 (in thousands):

	Amortized Cost Basis by Credit Rating - HTM Debt Securities
March 31, 2024	AAA		AA		A		BBB		BB		B		CCC-C		Total
State and political subdivisions:
Competitive	$	—	$	8,723	$	452,264	$	615,241	$	34,079	$	14,230	$	23,183	$	1,147,720
Utilities		604,178		929,491		102,810		27,464		401		—		—		1,664,344
Total state and political subdivisions	$	604,178	$	938,214	$	555,074	$	642,705	$	34,480	$	14,230	$	23,183	$	2,812,064

	Amortized Cost Basis by Credit Rating - HTM Debt Securities
December 31, 2023	AAA		AA		A		BBB		BB		B		CCC-C		Total
State and political subdivisions:
Competitive	$	—	$	7,704	$	464,349	$	641,743	$	30,734	$	15,326	$	2,649	$	1,162,505
Utilities		757,381		795,448		87,736		26,720		615		—		—		1,667,900
Total state and political subdivisions	$	757,381	$	803,152	$	552,085	$	668,463	$	31,349	$	15,326	$	2,649	$	2,830,405

Schedule of Other Securities

The table below provides detailed information for Other securities at March 31, 2024 and December 31, 2023 (in thousands):

	March 31, 2024		December 31, 2023
FRB and FHLB stock	$	87,672	$	87,672
Equity securities with readily determinable fair values		11,292		11,228
Equity securities without readily determinable fair values		374,470		394,035
Total	$	473,434	$	492,935

Schedule of Components of Investment Securities Gains (Losses), Net

The following table presents the components of Investments securities gains (losses), net for the three months ended March 31, 2024 and March 31, 2023 (in thousands):

	Three Months Ended March 31,
	2024			2023
Investment securities gain (losses), net
Available-for-sale debt securities:
Gains realized on sales	$	139		$	—
Losses realized on sales		—			(2	)
Impairment of AFS security		—			(4,800	)
Equity securities with readily determinable fair values:
Fair value adjustments, net		(23	)		88
Equity securities without readily determinable fair values:
Fair value adjustments, net		(450	)		(610	)
Sales		9,705			—
Total investment securities gains (losses), net	$	9,371		$	(5,324	)

Available-for-sale Securities [Member]

Contractual Maturity Information

The following table presents contractual maturity information for securities available for sale at March 31, 2024 (in thousands):

	Amortized		Fair
	Cost		Value
Due in 1 year or less	$	537,915	$	532,285
Due after 1 year through 5 years		1,322,690		1,291,442
Due after 5 years through 10 years		634,591		600,319
Due after 10 years		498,260		443,162
Total		2,993,456		2,867,208
Mortgage-backed securities		4,213,875		3,674,183
Total securities available for sale	$	7,207,331	$	6,541,391

Held-to-maturity Securities [Member]

Contractual Maturity Information

The following table provides detailed information about securities held to maturity at March 31, 2024 and December 31, 2023, respectively (in thousands):

March 31, 2024	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses			Net Carrying Amount
U.S. Agencies	$	123,240	$	—	$	(2,661	)	$	120,579	$	—		$	123,240
Mortgage-backed		2,691,133		—		(404,520	)		2,286,613		—			2,691,133
State and political subdivisions		2,812,064		15,957		(210,075	)		2,617,946		(3,820	)		2,808,244
Total	$	5,626,437	$	15,957	$	(617,256	)	$	5,025,138	$	(3,820	)	$	5,622,617

December 31, 2023	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses			Net Carrying Amount
U.S. Agencies	$	123,210	$	—	$	(2,686	)	$	120,524	$	—		$	123,210
Mortgage-backed		2,738,253		18		(356,657	)		2,381,614		—			2,738,253
State and political subdivisions		2,830,405		21,021		(170,197	)		2,681,229		(3,258	)		2,827,147
Total	$	5,691,868	$	21,039	$	(529,540	)	$	5,183,367	$	(3,258	)	$	5,688,610

The following table presents contractual maturity information for securities held to maturity at March 31, 2024 (in thousands):

	Amortized		Fair
	Cost		Value
Due in 1 year or less	$	104,769	$	103,830
Due after 1 year through 5 years		332,566		323,313
Due after 5 years through 10 years		826,088		784,857
Due after 10 years		1,671,881		1,526,525
Total		2,935,304		2,738,525
Mortgage-backed securities		2,691,133		2,286,613
Total securities held to maturity	$	5,626,437	$	5,025,138