Securities (Tables)

12 Months Ended

Dec. 31, 2023

Securities

Schedule of amortized cost and estimated fair value of securities

			Gross		Gross		Allowance		Estimated
	Amortized		Unrealized		Unrealized		for Credit		Fair
December 31, 2023	Cost		Gains		(Losses)		Losses		Value
	(Dollars in thousands)
Securities available-for-sale:
U.S. Treasury	$	387,990	$	—	$	(5,621)	$	—	$	382,369
Agency mortgage-backed securities		64,580		—		(4,313)		—		60,267
Total	$	452,570	$	—	$	(9,934)	$	—	$	442,636
			Gross		Gross		Estimated		Allowance
	Amortized		Unrecognized		Unrecognized		Fair		for Credit
December 31, 2023	Cost		Gains		(Losses)		Value		Losses
	(Dollars in thousands)
Securities held-to-maturity:
Agency mortgage-backed securities	$	618,374	$	282	$	(86,011)	$	532,645	$	—
Municipals - exempt from Federal tax		32,203		3		(724)		31,482		(12)
Total	$	650,577	$	285	$	(86,735)	$	564,127	$	(12)

			Gross		Gross		Allowance		Estimated
	Amortized		Unrealized		Unrealized		for Credit		Fair
December 31, 2022	Cost		Gains		(Losses)		Losses		Value
	(Dollars in thousands)
Securities available-for-sale:
U.S. Treasury	$	428,797	$	—	$	(10,323)	$	—	$	418,474
Agency mortgage-backed securities		76,916		—		(5,794)		—		71,122
Total	$	505,713	$	—	$	(16,117)	$	—	$	489,596
			Gross		Gross		Estimated		Allowance
	Amortized		Unrecognized		Unrecognized		Fair		for Credit
December 31, 2022	Cost		Gains		(Losses)		Value		Losses
	(Dollars in thousands)
Securities held-to-maturity:
Agency mortgage-backed securities	$	677,381	$	235	$	(99,977)	$	577,639	$	—
Municipals - exempt from Federal tax		37,623		9		(819)		36,813		(14)
Total	$	715,004	$	244	$	(100,796)	$	614,452	$	(14)

Schedule of securities with unrealized losses

	Less Than 12 Months				12 Months or More				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
December 31, 2023	Value		(Losses)		Value		(Losses)		Value		(Losses)
	(Dollars in thousands)
Securities available-for-sale:
U.S. Treasury	$	4,926	$	(40)	$	377,443	$	(5,581)	$	382,369	$	(5,621)
Agency mortgage-backed securities		—		—		60,267		(4,313)		60,267		(4,313)
Total	$	4,926	$	(40)	$	437,710	$	(9,894)	$	442,636	$	(9,934)
Securities held-to-maturity:
Agency mortgage-backed securities	$	—	$	—	$	520,615	$	(86,011)	$	520,615	$	(86,011)
Municipals — exempt from Federal tax		9,790		(176)		13,151		(548)		22,941		(724)
Total	$	9,790	$	(176)	$	533,766	$	(86,559)	$	543,556	$	(86,735)

	Less Than 12 Months				12 Months or More				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
December 31, 2022	Value		(Losses)		Value		(Losses)		Value		(Losses)
	(Dollars in thousands)
Securities available-for-sale:
U.S. Treasury	$	418,474	$	(10,323)	$	—	$	—	$	418,474	$	(10,323)
Agency mortgage-backed securities		71,122		(5,794)		—		—		71,122		(5,794)
Total	$	489,596	$	(16,117)	$	—	$	—	$	489,596	$	(16,117)
Securities held-to-maturity:
Agency mortgage-backed securities	$	136,264	$	(12,866)	$	429,257	$	(87,111)	$	565,521	$	(99,977)
Municipals — exempt from Federal tax		31,007		(819)		—		—		31,007		(819)
Total	$	167,271	$	(13,685)	$	429,257	$	(87,111)	$	596,528	$	(100,796)

Schedule of amortized cost and estimated fair values of securities, by contractual maturity

	Available-for-sale
	Amortized		Estimated
	Cost		Fair Value
	(Dollars in thousands)
Due three months or less	$	19,953	$	19,920
Due after three months through one year		193,476		191,662
Due after one through five years		174,561		170,787
Agency mortgage-backed securities		64,580		60,267
Total	$	452,570	$	442,636

	Held-to-maturity
	Amortized		Estimated
	Cost (1)		Fair Value
	(Dollars in thousands)
Due three months or less	$	400	$	400
Due after three months through one year		665		665
Due after one through five years		7,271		7,157
Due after five through ten years		23,867		23,260
Agency mortgage-backed securities		618,374		532,645
Total	$	650,577	$	564,127

Schedule of roll-forward by major security type of the allowance for credit losses on debt securities held-to-maturity

		Municipals
		(Dollars in thousands)
Beginning balance January 1, 2023	$	14
Recapture of credit losses		(2)
Ending balance December 31, 2023	$	12