Securities Available for Sale and Held to Maturity (Tables)

9 Months Ended

Sep. 30, 2021

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, 2021 and December 31, 2020 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
September 30, 2021	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	$	280,758	$	—	$	(2,143	)	$	278,615	$	—	$	—	$	—		$	—
U.S. Government agency    obligations		15,253		88		(362	)		14,979		—		—		—			—
Obligations of states and political    subdivisions		5,150		584		—			5,734		10,683		78		(4	)		10,757
Mortgage-backed securities
Residential mortgage pass-    through securities
Guaranteed by GNMA		42,772		1,100		(12	)		43,860		5,912		299		—			6,211
Issued by FNMA and    FHLMC		2,185,140		13,366		(11,094	)		2,187,412		48,554		1,468		—			50,022
Other residential mortgage-    backed securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		231,793		5,146		(54	)		236,885		264,638		13,143		(41	)		277,740
Commercial mortgage-backed    securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		292,428		731		(3,039	)		290,120		65,118		1,284		—			66,402
Total	$	3,053,294	$	21,015	$	(16,704	)	$	3,057,605	$	394,905	$	16,272	$	(45	)	$	411,132

	Securities Available for Sale									Securities Held to Maturity
December 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. Government agency    obligations	$	18,378	$	144	$	(481	)	$	18,041	$	—	$	—	$	—		$	—
Obligations of states and political    subdivisions		5,198		637		—			5,835		26,584		258		(3	)		26,839
Mortgage-backed securities
Residential mortgage pass-    through securities
Guaranteed by GNMA		55,193		1,672		(3	)		56,862		7,598		382		—			7,980
Issued by FNMA and    FHLMC		1,421,861		20,768		(1,308	)		1,441,321		67,944		2,397		—			70,341
Other residential mortgage-    backed securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		409,883		9,600		(46	)		419,437		360,361		19,678		(55	)		379,984
Commercial mortgage-backed    securities
Issued or guaranteed by    FNMA, FHLMC or    GNMA		49,260		1,068		(9	)		50,319		75,585		2,386		—			77,971
Total	$	1,959,773	$	33,889	$	(1,847	)	$	1,991,815	$	538,072	$	25,101	$	(58	)	$	563,115

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, 2021 and December 31, 2020 ($ in thousands):

	September 30, 2021		December 31, 2020
Aaa	$	384,222	$	511,488
Aa1 to Aa3		7,510		22,528
Not Rated (1)		3,173		4,056
Total	$	394,905	$	538,072

(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 and segregated by length of impairment at September 30, 2021 and December 31, 2020 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
September 30, 2021	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Treasury securities	$	278,615	$	(2,143	)	$	—	$	—		$	278,615	$	(2,143	)
U.S. Government agency obligations		—		—			9,355		(362	)		9,355		(362	)
Obligations of states and political subdivisions		5,506		(2	)		667		(2	)		6,173		(4	)
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		1,131		(12	)		—		—			1,131		(12	)
Issued by FNMA and FHLMC		1,553,063		(10,637	)		56,089		(457	)		1,609,152		(11,094	)
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		18,583		(95	)		—		—			18,583		(95	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		161,174		(3,030	)		644		(9	)		161,818		(3,039	)
Total	$	2,018,072	$	(15,919	)	$	66,755	$	(830	)	$	2,084,827	$	(16,749	)
December 31, 2020
U.S. Government agency obligations	$	—	$	—		$	11,167	$	(481	)	$	11,167	$	(481	)
Obligations of states and political subdivisions		—		—			667		(3	)		667		(3	)
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		1,636		(3	)		—		—			1,636		(3	)
Issued by FNMA and FHLMC		324,905		(1,308	)		—		—			324,905		(1,308	)
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		29,398		(101	)		—		—			29,398		(101	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		—		—			659		(9	)		659		(9	)
Total	$	355,939	$	(1,412	)	$	12,493	$	(493	)	$	368,432	$	(1,905	)

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, 2021, 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	$	1,709	$	1,729	$	6,161	$	6,186
Due after one year through five years		189,184		188,236		4,522		4,571
Due after five years through ten years		94,838		93,690		—		—
Due after ten years		15,430		15,673		—		—
		301,161		299,328		10,683		10,757
Mortgage-backed securities		2,752,133		2,758,277		384,222		400,375
Total	$	3,053,294	$	3,057,605	$	394,905	$	411,132