Securities Available for Sale and Held to Maturity (Tables)

12 Months Ended

Dec. 31, 2023

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 December 31, 2023 and 2022 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
			Gross		Gross			Estimated				Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair		Amortized		Unrealized		Unrealized			Fair
December 31, 2023	Cost		Gains		Losses			Value		Cost		Gains		Losses			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
December 31, 2022
U.S. Treasury securities	$	425,719	$	308	$	(34,514	)	$	391,513	$	28,295	$	—	$	(115	)	$	28,180
U.S. Government agency obligations		8,297		—		(531	)		7,766		—		—		—			—
Obligations of states and political    subdivisions		4,820		53		(11	)		4,862		4,510		3		(3	)		4,510
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		30,534		7		(3,444	)		27,097		4,442		—		(395	)		4,047
Issued by FNMA and FHLMC		1,541,570		12		(196,119	)		1,345,463		509,311		—		(19,586	)		489,725
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		123,755		—		(8,615	)		115,140		188,201		—		(13,826	)		174,375
Commercial mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		136,014		—		(3,773	)		132,241		759,755		34		(54,037	)		705,752
Total	$	2,270,709	$	380	$	(247,007	)	$	2,024,082	$	1,494,514	$	37	$	(87,962	)	$	1,406,589

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 December 31, 2023 and 2022 ($ in thousands):

	December 31, 2023		December 31, 2022
Aaa	$	1,425,939	$	1,490,004
Aa1 to Aa3		—		3,001
Not Rated (1)		340		1,509
Total	$	1,426,279	$	1,494,514

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

Securities with Gross Unrealized Losses, Segregated by Length of Impairment

The table below includes securities with gross unrealized losses for which an ACL has not been recorded and segregated by length of impairment at December 31, 2023 and 2022 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
			Gross					Gross					Gross
	Estimated		Unrealized			Estimated		Unrealized			Estimated		Unrealized
December 31, 2023	Fair Value		Losses			Fair Value		Losses			Fair Value		Losses
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	)
December 31, 2022
U.S. Treasury securities	$	161,298	$	(5,655	)	$	258,087	$	(28,974	)	$	419,385	$	(34,629	)
U.S. Government agency obligations		1,828		(184	)		5,938		(347	)		7,766		(531	)
Obligations of states and political    subdivisions		1,017		(11	)		3,664		(3	)		4,681		(14	)
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		27,223		(3,270	)		3,577		(569	)		30,800		(3,839	)
Issued by FNMA and FHLMC		770,865		(41,807	)		1,062,041		(173,898	)		1,832,906		(215,705	)
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		281,964		(21,452	)		7,235		(989	)		289,199		(22,441	)
Commercial mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		833,970		(57,742	)		1,644		(68	)		835,614		(57,810	)
Total	$	2,078,165	$	(130,121	)	$	1,342,186	$	(204,848	)	$	3,420,351	$	(334,969	)

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

For the years ended December 31, 2023, 2022 and 2021, gross realized gains or losses as a result of calls and dispositions of securities, as well as any associated proceeds, were as follows ($ in thousands):

	Years Ended December 31,
Available for Sale	2023			2022		2021
Proceeds from calls and sales of securities	$	4,796		$	—	$	—
Gross realized gains		47			—		—
Gross realized losses		(8	)		—		—

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 December 31, 2023, 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				Securities
	Available for Sale				Held to Maturity
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	65,199	$	63,501	$	340	$	340
Due after one year through five years		331,225		309,108		29,068		29,042
Due after five years through ten years		2,356		2,151		—		—
Due after ten years		3,606		3,400		—		—
		402,386		378,160		29,408		29,382
Mortgage-backed securities		1,556,621		1,384,718		1,396,871		1,326,122
Total	$	1,959,007	$	1,762,878	$	1,426,279	$	1,355,504