Investment Securities (Tables)

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-Sale Securities and Held-to-Maturity Securities

The amortized cost and estimated fair value of the Company's available-for-sale and held-to-maturity securities are summarized as follows:

(dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Estimated Fair Value
March 31, 2024
Investment securities available-for-sale:
U.S. treasury bonds	$	49,919	$	—	$	(1,686)	$	—	$	48,233
U.S. agency securities	698,189		—		(58,863)		—		639,326
Residential mortgage-backed securities	800,793		23		(102,266)		—		698,550
Commercial mortgage-backed securities	54,018		—		(5,080)		—		48,938
Municipal bonds	8,740		—		(434)		—		8,306
Corporate bonds	2,000		—		(302)		(17)		1,681
Total available-for-sale securities	$	1,613,659	$	23	$	(168,631)	$	(17)	$	1,445,034

(dollars in thousands)	Amortized Cost		Gross Unrecognized Gains		Gross Unrecognized Losses		Estimated Fair Value
March 31, 2024
Investment securities held-to-maturity:
Residential mortgage-backed securities	$	655,388	$	—	$	(87,348)	$	568,040
Commercial mortgage-backed securities	89,966		—		(13,000)		76,966
Municipal bonds	125,003		—		(9,789)		115,214
Corporate bonds	132,332		—		(14,393)		117,939
Total	$	1,002,689	$	—	$	(124,530)	$	878,159
Allowance for credit losses	(1,957)
Total held-to-maturity securities, net of ACL	$	1,000,732

(dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Estimated Fair Value
December 31, 2023
Investment securities available-for-sale:
U.S. treasury bonds	$	49,894	$	—	$	(1,993)	$	—	$	47,901
U.S. agency securities	729,090		—		(57,693)		—		671,397
Residential mortgage-backed securities	823,992		45		(96,684)		—		727,353
Commercial mortgage-backed securities	54,557		—		(4,993)		—		49,564
Municipal bonds	8,783		—		(293)		—		8,490
Corporate bonds	2,000		—		(300)		(17)		1,683
Total available-for-sale securities	$	1,668,316	$	45	$	(161,956)	$	(17)	$	1,506,388

(dollars in thousands)	Amortized Cost		Gross Unrecognized Gains		Gross Unrecognized Losses		Estimated Fair Value
December 31, 2023
Investment securities held-to-maturity:
Residential mortgage-backed securities	$	670,043	$	—	$	(79,980)	$	590,063
Commercial mortgage-backed securities	90,227		—		(12,867)		77,360
Municipal bonds	125,114		5		(8,540)		116,579
Corporate bonds	132,309		—		(14,729)		117,580
Total	$	1,017,693	$	5	$	(116,116)	$	901,582
Allowance for credit losses	(1,956)
Total held-to-maturity securities, net of ACL	$	1,015,737

Schedule of Gross Unrealized Losses and Fair Value by Length of Time that the Individual Available-For-Sale Securities Have Been in a Continuous Unrealized Loss

The following tables summarize available-for-sale and held-to-maturity securities in an unrealized loss position by length of time:

		Less Than 12 Months				12 Months or Greater				Total
(dollars in thousands)	Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
March 31, 2024
Investment securities available-for-sale:
U.S. treasury bonds	2	$	—	$	—	$	48,233	$	(1,686)	$	48,233	$	(1,686)
U. S. agency securities	76	2,904		(5)		636,422		(58,858)		639,326		(58,863)
Residential mortgage-backed securities	151	8,180		(60)		688,525		(102,206)		696,705		(102,266)
Commercial mortgage-backed securities	13	—		—		48,938		(5,080)		48,938		(5,080)
Municipal bonds	1	—		—		8,306		(434)		8,306		(434)
Corporate bonds	1	—		—		1,681		(302)		1,681		(302)
Total	244	$	11,084	$	(65)	$	1,432,105	$	(168,566)	$	1,443,189	$	(168,631)

		Less Than 12 Months				12 Months or Greater				Total
(dollars in thousands)	Number of Securities	Estimated Fair Value		Unrecognized Losses		Estimated Fair Value		Unrecognized Losses		Estimated Fair Value		Unrecognized Losses
March 31, 2024
Investment securities held-to-maturity:
Residential mortgage-backed securities	142	$	—	$	—	$	568,040	$	(87,348)	$	568,040	$	(87,348)
Commercial mortgage-backed securities	16	—		—		76,966		(13,000)		76,966		(13,000)
Municipal bonds	42	3,474		(63)		111,740		(9,726)		115,214		(9,789)
Corporate bonds	30	—		—		105,887		(14,393)		105,887		(14,393)
Total	230	$	3,474	$	(63)	$	862,633	$	(124,467)	$	866,107	$	(124,530)

		Less Than 12 Months				12 Months or Greater				Total
(dollars in thousands)	Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
December 31, 2023
Investment securities available-for-sale:
U.S. treasury bonds	2	$	—	$	—	$	47,901	$	(1,993)	$	47,901	$	(1,993)
U. S. agency securities	78	3,084		(4)		668,313		(57,689)		671,397		(57,693)
Residential mortgage-backed securities	149	—		—		718,042		(96,684)		718,042		(96,684)
Commercial mortgage-backed securities	13	—		—		49,564		(4,993)		49,564		(4,993)
Municipal bonds	1	—		—		8,490		(293)		8,490		(293)
Corporate bonds	1	—		—		1,683		(300)		1,683		(300)
Total	244	$	3,084	$	(4)	$	1,493,993	$	(161,952)	$	1,497,077	$	(161,956)

		Less Than 12 Months				12 Months or Greater				Total
(dollars in thousands)	Number of Securities	Estimated Fair Value		Unrecognized Losses		Estimated Fair Value		Unrecognized Losses		Estimated Fair Value		Unrecognized Losses
December 31, 2023
Investment securities held-to-maturity:
Residential mortgage-backed securities	142	$	—	$	—	$	590,063	$	(79,980)	$	590,063	$	(79,980)
Commercial mortgage-backed securities	16	—		—		77,360		(12,867)		77,360		(12,867)
Municipal bonds	40	—		—		113,031		(8,540)		113,031		(8,540)
Corporate bonds	30	—		—		105,523		(14,729)		105,523		(14,729)
Total	228	$	—	$	—	$	885,977	$	(116,116)	$	885,977	$	(116,116)

Schedule of Amortized Cost and Estimated Fair Value of Investments Available-for-Sale by Contractual Maturity

The following table summarizes the Company's investment securities available-for-sale and investment securities held-to-maturity by contractual maturity. Expected maturities for mortgage-backed securities ("MBS") will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	March 31, 2024
(dollars in thousands)	Amortized Cost		Estimated Fair Value
Investment securities available-for-sale:
Within one year	$	139,224	$	135,426
One to five years	486,394		446,955
Five to ten years	112,838		97,570
Beyond ten years	20,392		17,612
Residential mortgage-backed securities	800,793		698,550
Commercial mortgage-backed securities	54,018		48,938
Less: allowance for credit losses	—		(17)
Total investment securities available-for-sale	1,613,659		1,445,034
Investment securities held-to-maturity:
Within one year	4,282		4,247
One to five years	61,707		59,309
Five to ten years	117,237		102,274
Beyond ten years	74,109		67,323
Residential mortgage-backed securities:	655,388		568,040
Commercial mortgage-backed securities	89,966		76,966
Less: allowance for credit losses	(1,957)		—
Total investment securities held-to-maturity	1,000,732		878,159
Total	$	2,614,391	$	2,323,193