Securities (Tables)

9 Months Ended

Sep. 30, 2023

Securities Available for Sale

This table provides detailed information about securities available for sale at September 30, 2023 and December 31, 2022 (in thousands):

September 30, 2023	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	797,238	$	—	$	(17,863	)	$	779,375
U.S. Agencies		178,037		—		(4,687	)		173,350
Mortgage-backed		4,175,240		—		(695,289	)		3,479,951
State and political subdivisions		1,367,097		51		(160,492	)		1,206,656
Corporates		382,914		—		(38,013	)		344,901
Collateralized loan obligations		347,999		536		(2,069	)		346,466
Total	$	7,248,525	$	587	$	(918,413	)	$	6,330,699

December 31, 2022	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	804,158	$	58	$	(27,146	)	$	777,070
U.S. Agencies		178,261		—		(6,965	)		171,296
Mortgage-backed		4,574,905		92		(592,875	)		3,982,122
State and political subdivisions		1,465,598		1,608		(104,799	)		1,362,407
Corporates		401,059		—		(33,559	)		367,500
Collateralized loan obligations		353,969		32		(8,049	)		345,952
Total	$	7,777,950	$	1,790	$	(773,393	)	$	7,006,347

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 September 30, 2023 and December 31, 2022 (in thousands):

	Less than 12 months							12 months or more							Total
September 30, 2023	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury		6	$	42,600	$	(322	)		63	$	736,775	$	(17,541	)		69	$	779,375	$	(17,863	)
U.S. Agencies		—		—		—			29		173,350		(4,687	)		29		173,350		(4,687	)
Mortgage-backed		18		27,783		(1,595	)		856		3,452,081		(693,694	)		874		3,479,864		(695,289	)
State and political subdivisions		617		332,747		(18,712	)		1,517		864,436		(141,780	)		2,134		1,197,183		(160,492	)
Corporates		—		—		—			267		344,901		(38,013	)		267		344,901		(38,013	)
Collateralized loan obligations		1		4,245		(5	)		34		231,032		(2,064	)		35		235,277		(2,069	)
Total		642	$	407,375	$	(20,634	)		2,766	$	5,802,575	$	(897,779	)		3,408	$	6,209,950	$	(918,413	)

	Less than 12 months							12 months or more							Total
December 31, 2022	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury		61	$	688,208	$	(22,731	)		4	$	55,314	$	(4,415	)		65	$	743,522	$	(27,146	)
U.S. Agencies		27		140,877		(4,734	)		2		30,419		(2,231	)		29		171,296		(6,965	)
Mortgage-backed		687		1,415,169		(102,881	)		205		2,557,035		(489,994	)		892		3,972,204		(592,875	)
State and political subdivisions		1,744		936,865		(51,427	)		273		233,679		(53,372	)		2,017		1,170,544		(104,799	)
Corporates		86		146,615		(8,783	)		189		216,885		(24,776	)		275		363,500		(33,559	)
Collateralized loan obligations		41		326,659		(7,820	)		1		4,785		(229	)		42		331,444		(8,049	)
Total		2,646	$	3,654,393	$	(198,376	)		674	$	3,098,117	$	(575,017	)		3,320	$	6,752,510	$	(773,393	)

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 September 30, 2023 and December 31, 2022, respectively (in thousands):

	Less than 12 months							12 months or more							Total
September 30, 2023	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
U.S. Agencies		—	$	—	$	—			11	$	118,952	$	(4,228	)		11	$	118,952	$	(4,228	)
Mortgage-backed		8		7,460		(435	)		261		2,270,212		(511,996	)		269		2,277,672		(512,431	)
State and political subdivisions		186		527,731		(53,443	)		1,382		1,688,475		(312,849	)		1,568		2,216,206		(366,292	)
Total		194	$	535,191	$	(53,878	)		1,654	$	4,077,639	$	(829,073	)		1,848	$	4,612,830	$	(882,951	)

	Less than 12 months							12 months or more							Total
December 31, 2022	Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses			Count		Fair Value		Unrealized Losses
U.S. Agency		11	$	118,524	$	(4,567	)		—	$	—	$	—			11	$	118,524	$	(4,567	)
Mortgage-backed		254		2,342,656		(346,611	)		11		228,079		(45,919	)		265		2,570,735		(392,530	)
State and political subdivisions		1,403		1,543,692		(177,957	)		61		617,805		(23,515	)		1,464		2,161,497		(201,472	)
Total		1,668	$	4,004,872	$	(529,135	)		72	$	845,884	$	(69,434	)		1,740	$	4,850,756	$	(598,569	)

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 investments at September 30, 2023 and December 31, 2022 (in thousands):

	Amortized Cost Basis by Credit Rating - HTM Debt Securities
September 30, 2023	AAA		AA		A		BBB		BB		B		CCC-C		Total
State and political subdivisions:
Competitive	$	—	$	6,588	$	460,569	$	645,173	$	14,490	$	16,170	$	2,721	$	1,145,711
Utilities		757,467		795,802		91,160		28,554		606		—		—		1,673,589
Total state and political subdivisions	$	757,467	$	802,390	$	551,729	$	673,727	$	15,096	$	16,170	$	2,721	$	2,819,300

	Amortized Cost Basis by Credit Rating - HTM Debt Securities
December 31, 2022	AAA		AA		A		BBB		BB		CCC-C		Total
State and political subdivisions:
Competitive	$	—	$	—	$	435,953	$	618,517	$	17,120	$	2,934	$	1,074,524
Utilities		759,539		824,386		84,293		29,599		581		—		1,698,398
Total state and political subdivisions	$	759,539	$	824,386	$	520,246	$	648,116	$	17,701	$	2,934	$	2,772,922

Schedule of Other Securities

The table below provides detailed information for Other securities at September 30, 2023 and December 31, 2022 (in thousands):

	September 30, 2023		December 31, 2022
FRB and FHLB stock	$	102,672	$	41,472
Equity securities with readily determinable fair values		10,780		10,782
Equity securities without readily determinable fair values		359,803		297,504
Total	$	473,255	$	349,758

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

The table below presents the components of Investments securities gains (losses), net for the three and nine months ended September 30, 2023 and September 30, 2022 (in thousands):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Investment securities gain (losses), net
Available-for-sale debt securities:
Gains realized on sales	$	154		$	—		$	154		$	—
Losses realized on sales		—			—			(2	)		—
Impairment of AFS security		—			—			(4,925	)		—
Equity securities with readily determinable fair values:
Fair value adjustments, net		(223	)		(1,441	)		(197	)		(8,570	)
Equity securities without readily determinable fair values:
Fair value adjustments, net		340			96			817			1,261
Sales		—			—			—			66,162
Total investment securities gains (losses), net	$	271		$	(1,345	)	$	(4,153	)	$	58,853

Available-for-sale Securities [Member]

Contractual Maturity Information

The following table presents contractual maturity information for securities available for sale at September 30, 2023 (in thousands):

	Amortized		Fair
	Cost		Value
Due in 1 year or less	$	833,933	$	821,161
Due after 1 year through 5 years		1,017,582		966,945
Due after 5 years through 10 years		713,019		649,262
Due after 10 years		508,751		413,380
Total		3,073,285		2,850,748
Mortgage-backed securities		4,175,240		3,479,951
Total securities available for sale	$	7,248,525	$	6,330,699

Held-to-maturity Securities [Member]

Contractual Maturity Information

The following table provides detailed information about securities held to maturity at September 30, 2023 and December 31, 2022, respectively (in thousands):

September 30, 2023	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses			Net Carrying Amount
U.S. Agencies	$	123,180	$	—	$	(4,228	)	$	118,952	$	—		$	123,180
Mortgage-backed		2,790,103		—		(512,431	)		2,277,672		—			2,790,103
State and political subdivisions		2,819,300		6,834		(366,292	)		2,459,842		(2,886	)		2,816,414
Total	$	5,732,583	$	6,834	$	(882,951	)	$	4,856,466	$	(2,886	)	$	5,729,697

December 31, 2022	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses			Net Carrying Amount
U.S. Agencies	$	123,091	$	—	$	(4,567	)	$	118,524	$	—		$	123,091
Mortgage-backed		2,965,586		11		(392,530	)		2,573,067		—			2,965,586
State and political subdivisions		2,772,922		17,618		(201,472	)		2,589,068		(2,407	)		2,770,515
Total	$	5,861,599	$	17,629	$	(598,569	)	$	5,280,659	$	(2,407	)	$	5,859,192

The following table presents contractual maturity information for securities held to maturity at September 30, 2023 (in thousands):

	Amortized		Fair
	Cost		Value
Due in 1 year or less	$	84,409	$	83,964
Due after 1 year through 5 years		328,485		317,451
Due after 5 years through 10 years		824,540		757,544
Due after 10 years		1,705,046		1,419,835
Total		2,942,480		2,578,794
Mortgage-backed securities		2,790,103		2,277,672
Total securities held to maturity	$	5,732,583	$	4,856,466