Securities Available for Sale and Held to Maturity (Tables)

9 Months Ended

Sep. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Amortized Cost and Estimated Fair Value of Available for Sale and Held to Maturity Securities

The following tables are a summary of the amortized cost and estimated fair value of securities available for sale and held to maturity at September 30, 2024 and December 31, 2023 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
September 30, 2024	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. Treasury securities	$	198,426	$	4,212	$	—		$	202,638	$	29,648	$	232	$	—		$	29,880
U.S. Government agency    obligations		19,494		—		(159	)		19,335		—		—		—			—
Mortgage-backed securities
Residential mortgage pass-    through securities
Guaranteed by GNMA		27,787		15		(2,004	)		25,798		17,773		3		(407	)		17,369
Issued by FNMA and    FHLMC		1,086,688		32,970		(14,348	)		1,105,310		436,177		2,104		(11,088	)		427,193
Other residential mortgage-    backed securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		—		—		—			—		131,348		—		(6,179	)		125,169
Commercial mortgage-backed    securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		359,160		14,326		(772	)		372,714		743,412		139		(26,995	)		716,556
Total	$	1,691,555	$	51,523	$	(17,283	)	$	1,725,795	$	1,358,358	$	2,478	$	(44,669	)	$	1,316,167

	Securities Available for Sale									Securities Held to Maturity
December 31, 2023	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. Treasury Securities	$	396,179	$	—	$	(23,811	)	$	372,368	$	29,068	$	—	$	(26	)	$	29,042
U.S. Government agency    obligations		6,207		1		(416	)		5,792		—		—		—			—
Obligations of states and    political subdivisions		—		—		—			—		340		—		—			340
Mortgage-backed securities
Residential mortgage pass-    through securities
Guaranteed by GNMA		25,744		4		(2,613	)		23,135		13,005		—		(497	)		12,508
Issued by FNMA and    FHLMC		1,338,256		32		(161,490	)		1,176,798		469,593		—		(18,205	)		451,388
Other residential mortgage-    backed securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		92,076		—		(6,002	)		86,074		154,466		—		(10,113	)		144,353
Commercial mortgage-backed    securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		100,545		—		(1,834	)		98,711		759,807		51		(41,985	)		717,873
Total	$	1,959,007	$	37	$	(196,166	)	$	1,762,878	$	1,426,279	$	51	$	(70,826	)	$	1,355,504

Securities Held to Maturity by Credit Rating, as Determined by Moody's

The following table presents the amortized cost of Trustmark’s securities held to maturity by credit rating, as determined by Moody’s, at September 30, 2024 and December 31, 2023 ($ in thousands):

	September 30, 2024		December 31, 2023
Aaa	$	1,358,358	$	1,425,939
Not Rated (1)		—		340
Total	$	1,358,358	$	1,426,279

(1) Not rated securities primarily consist of Mississippi municipal general obligations.

Securities with Gross Unrealized Losses, Segregated by Length of Impairment

The tables below include securities with gross unrealized losses for which an allowance for credit losses has not been recorded segregated by length of impairment at September 30, 2024 and December 31, 2023 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
September 30, 2024	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Government agency obligations	$	19,335	$	(159	)	$	—	$	—		$	19,335	$	(159	)
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		11,089		(51	)		29,760		(2,360	)		40,849		(2,411	)
Issued by FNMA and FHLMC		18,133		(72	)		254,346		(25,364	)		272,479		(25,436	)
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		—		—			125,169		(6,179	)		125,169		(6,179	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		—		—			792,767		(27,767	)		792,767		(27,767	)
Total	$	48,557	$	(282	)	$	1,202,042	$	(61,670	)	$	1,250,599	$	(61,952	)
December 31, 2023
U.S. Treasury Securities	$	29,042	$	(26	)	$	372,368	$	(23,811	)	$	401,410	$	(23,837	)
U.S. Government agency obligations		—		—			5,791		(416	)		5,791		(416	)
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		9,381		(172	)		25,967		(2,938	)		35,348		(3,110	)
Issued by FNMA and FHLMC		309,466		(3,274	)		1,311,865		(176,421	)		1,621,331		(179,695	)
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		—		—			230,368		(16,115	)		230,368		(16,115	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		1,656		(13	)		812,520		(43,806	)		814,176		(43,819	)
Total	$	349,545	$	(3,485	)	$	2,758,879	$	(263,507	)	$	3,108,424	$	(266,992	)

Gains and Losses as a Result of Calls and Disposition of Securities

For the periods presented, gross realized losses as a result of calls and dispositions of securities, as well as any associated proceeds, are shown below ($ in thousands). There were no gross realized gains during the periods presented.

	Three Months Ended September 30,				Nine Months Ended September 30,
Available for Sale	2024		2023		2024			2023
Proceeds from calls and sales of securities	$	—	$	—	$	1,378,272		$	—
Gross realized (losses)		—		—		(182,792	)		—

Contractual Maturities of Available for Sale and Held to Maturity Securities

The amortized cost and estimated fair value of securities available for sale and held to maturity at September 30, 2024, by contractual maturity, are shown below ($ in thousands). Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	Securities Available for Sale				Securities Held to Maturity
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	42,751	$	42,962	$	—	$	—
Due after one year through five years		75,223		76,656		29,648		29,880
Due after five years through ten years		99,946		102,355		—		—
		217,920		221,973		29,648		29,880
Mortgage-backed securities		1,473,635		1,503,822		1,328,710		1,286,287
Total	$	1,691,555	$	1,725,795	$	1,358,358	$	1,316,167