Investment Securities (Tables)

3 Months Ended

Mar. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-Sale 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, 2023
Investment securities available-for-sale:
U.S. treasury bonds	$	49,818	$	—	$	(2,887)	$	—	$	46,931
U.S. agency securities	741,694		—		(67,227)		—		674,467
Residential mortgage-backed securities	905,524		76		(105,358)		—		800,242
Commercial mortgage-backed securities	55,421		—		(5,139)		—		50,282
Municipal bonds	8,914		—		(432)		—		8,482
Corporate bonds	2,000		—		(188)		(31)		1,781
Total available-for-sale securities	$	1,763,371	$	76	$	(181,231)	$	(31)	$	1,582,185

(dollars in thousands)	Amortized Cost		Gross Unrecognized Gains		Gross Unrecognized Losses		Estimated Fair Value
March 31, 2023
Investment securities held-to-maturity:
Residential mortgage-backed securities	$	724,756	$	—	$	(77,286)	$	647,470
Commercial mortgage-backed securities	92,141		—		(11,234)		80,907
Municipal bonds	128,160		—		(8,690)		119,470
Corporate bonds	132,254		—		(14,315)		117,939
Total	$	1,077,311	$	—	$	(111,525)	$	965,786
Allowance for credit losses	(2,008)
Total held-to-maturity securities, net of ACL	$	1,075,303

(dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Estimated Fair Value
December 31, 2022
Investment securities available-for-sale:
U.S. treasury bonds	$	49,793	$	—	$	(3,466)	$	—	$	46,327
U.S. agency securities	747,777		—		(78,049)		—		669,728
Residential mortgage-backed securities	937,557		18		(117,072)		—		820,503
Commercial mortgage-backed securities	56,071		—		(5,858)		—		50,213
Municipal bonds	10,700		45		(658)		—		10,087
Corporate bonds	2,000		—		(175)		(17)		1,808
Total available-for-sale securities	$	1,803,898	$	63	$	(205,278)	$	(17)	$	1,598,666

(dollars in thousands)	Amortized Cost		Gross Unrecognized Gains		Gross Unrecognized Losses		Estimated Fair Value
December 31, 2022
Investment securities held-to-maturity:
Residential mortgage-backed securities	$	741,057	$	—	$	(88,390)	$	652,667
Commercial mortgage-backed securities	92,557		—		(11,993)		80,564
Municipal bonds	128,273		—		(12,092)		116,181
Corporate bonds	132,253		—		(12,958)		119,295
Total	$	1,094,140	$	—	$	(125,433)	$	968,707
Allowance for credit losses	(766)
Total held-to-maturity securities, net of ACL	$	1,093,374

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 summarizes 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, 2023
Investment securities available-for-sale:
U.S. treasury bonds	2	$	—	$	—	$	46,931	$	(2,887)	$	46,931	$	(2,887)
U. S. agency securities	79	499,312		(50,108)		175,155		(17,119)		674,467		(67,227)
Residential mortgage-backed securities	158	—		—		800,166		(105,358)		800,166		(105,358)
Commercial mortgage-backed securities	13	—		—		50,282		(5,139)		50,282		(5,139)
Municipal bonds	1	—		—		8,482		(432)		8,482		(432)
Corporate bonds	1	—		—		1,812		(188)		1,812		(188)
Total	254	$	499,312	$	(50,108)	$	1,082,828	$	(131,123)	$	1,582,140	$	(181,231)

		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, 2023
Investment securities held-to-maturity:
Residential mortgage-backed securities	143	$	—	$	—	$	647,470	$	(77,286)	$	647,470	$	(77,286)
Commercial mortgage-backed securities	16	—		—		80,907		(11,234)		80,907		(11,234)
Municipal bonds	43	3,122		(29)		116,348		(8,661)		119,470		(8,690)
Corporate bonds	32	21,367		(2,596)		96,572		(11,719)		117,939		(14,315)
Total	234	$	24,489	$	(2,625)	$	941,297	$	(108,900)	$	965,786	$	(111,525)

		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, 2022
Investment securities available-for-sale:
U.S. treasury bond	2	$	—	$	—	$	46,327	$	(3,466)	$	46,327	$	(3,466)
U. S. agency securities	85	490,699		(58,437)		179,029		(19,612)		669,728		(78,049)
Residential mortgage-backed securities	157	3,994		—		808,697		(117,072)		812,691		(117,072)
Commercial mortgage-backed securities	14	471		(2)		49,742		(5,856)		50,213		(5,858)
Municipal bonds	1	—		—		8,299		(658)		8,299		(658)
Corporate bonds	1	—		—		1,825		(175)		1,825		(175)
Total	260	$	495,164	$	(58,439)	$	1,093,919	$	(146,839)	$	1,589,083	$	(205,278)

		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, 2022
Investment securities held-to-maturity:
Residential mortgage-backed securities	143	$	—	$	—	$	652,667	$	(88,390)	$	652,667	$	(88,390)
Commercial mortgage-backed securities	16	—		—		80,564		(11,993)		80,564		(11,993)
Municipal bonds	43	3,110		(45)		113,071		(12,047)		116,181		(12,092)
Corporate bonds	30	20,771		(3,183)		86,451		(9,775)		107,222		(12,958)
Total	232	$	23,881	$	(3,228)	$	932,753	$	(122,205)	$	956,634	$	(125,433)

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

The amortized cost and estimated fair value of available-for-sale and held-to-maturity securities at March 31, 2023 and December 31, 2022 by contractual maturity are shown in the table below. Contractual maturities for mortgage-backed securities ("MBS") are excluded as they may differ significantly from expected maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	March 31, 2023				December 31, 2022
	Amortized		Estimated		Amortized		Estimated
(dollars in thousands)	Cost (1)		Fair Value		Cost		Fair Value
Investment securities available-for-sale
U. S. agency securities maturing:
One year or less	549,420		499,312		$	549,137	$	490,699
After one year through five years	110,918		100,911		111,742		100,297
After five years through ten years	68,936		64,008		73,886		68,180
After ten years	12,420		10,236		13,012		10,552
Residential mortgage-backed securities:	905,524		800,242		937,557		820,503
Commercial mortgage-backed securities	55,421		50,282		56,071		50,213
Municipal bonds maturing:
One year or less	—		—		300		300
After one year through five years	—		—		1,444		1,488
After five years through ten years	8,914		8,482		8,956		8,299
After ten years	—		—		—		—
Corporate bonds maturing:
One year or less	—		—		—		—
After one year through five years	2,000		1,812		2,000		1,825
After five years through ten years	—		—		—		—
U.S. Treasury	49,818		46,931		49,793		46,327
Allowance for credit losses	—		(31)		—		(17)
	1,763,371		1,582,185		1,803,898		1,598,666
Investment securities held-to-maturity
Residential mortgage-backed securities:	724,756		647,470		741,057		652,667
Commercial mortgage-backed securities	92,141		80,907		92,557		80,564
Municipal bonds maturing:
One year or less	3,151		3,122		3,139		3,110
After one year through five years	35,520		34,398		35,579		33,743
After five years through ten years	77,246		70,370		77,262		67,945
After ten years	12,243		11,580		12,293		11,383
Corporate bonds maturing:
One year or less	23,963		21,367		23,954		20,771
After one year through five years	84,938		75,735		84,953		77,997
After five years through ten years	23,353		20,837		23,346		20,527
Allowance for credit losses	(2,008)		—		(766)		—
	1,075,303		965,786		1,093,374		968,707
	$	2,838,674	$	2,547,971	$	2,897,272	$	2,567,373

(1)Amortized cost for investment securities held-to-maturity is presented net of the allowance for credit losses on the Consolidated Balance Sheet.