Securities Available for Sale and Held to Maturity (Tables)

3 Months Ended

Mar. 31, 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 March 31, 2024 and December 31, 2023 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
March 31, 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	$	396,289	$	—	$	(23,865	)	$	372,424	$	29,261	$	—	$	(515	)	$	28,746
U.S. Government agency    obligations		6,017		—		(423	)		5,594		—		—		—			—
Obligations of states and    political subdivisions		—		—		—			—		340		—		—			340
Mortgage-backed securities
Residential mortgage pass-    through securities
Guaranteed by GNMA		25,343		6		(3,117	)		22,232		18,387		—		(750	)		17,637
Issued by FNMA and    FHLMC		1,293,149		22		(163,650	)		1,129,521		461,457		46		(21,935	)		439,568
Other residential mortgage-    backed securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		85,317		—		(6,218	)		79,099		146,447		—		(10,731	)		135,716
Commercial mortgage-backed    securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		94,865		—		(1,436	)		93,429		759,133		13		(48,139	)		711,007
Total	$	1,900,980	$	28	$	(198,709	)	$	1,702,299	$	1,415,025	$	59	$	(82,070	)	$	1,333,014

	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 March 31, 2024 and December 31, 2023 ($ in thousands):

	March 31, 2024		December 31, 2023
Aaa	$	1,414,685	$	1,425,939
Not Rated (1)		340		340
Total	$	1,415,025	$	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 March 31, 2024 and December 31, 2023 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
March 31, 2024	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Treasury securities	$	28,746	$	(515	)	$	372,424	$	(23,865	)	$	401,170	$	(24,380	)
U.S. Government agency obligations		—		—			5,594		(423	)		5,594		(423	)
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		14,632		(343	)		24,950		(3,524	)		39,582		(3,867	)
Issued by FNMA and FHLMC		303,034		(5,957	)		1,259,726		(179,628	)		1,562,760		(185,585	)
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		—		—			214,805		(16,949	)		214,805		(16,949	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		1,616		(55	)		800,447		(49,520	)		802,063		(49,575	)
Total	$	348,028	$	(6,870	)	$	2,677,946	$	(273,909	)	$	3,025,974	$	(280,779	)
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	)

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 March 31, 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	$	99,995	$	98,050	$	340	$	340
Due after one year through five years		296,508		274,584		29,261		28,746
Due after five years through ten years		2,236		2,021		—		—
Due after ten years		3,567		3,363		—		—
		402,306		378,018		29,601		29,086
Mortgage-backed securities		1,498,674		1,324,281		1,385,424		1,303,928
Total	$	1,900,980	$	1,702,299	$	1,415,025	$	1,333,014