Securities - Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Securities (Details) - USD ($) $ in Thousands		Mar. 31, 2024		Dec. 31, 2023		Dec. 31, 2022
Available-for-Sale Securities:
Amortized Cost		$ 137,119		$ 139,781
Gross Unrealized Losses		(21,075)		(19,879)
Fair Value		116,044		119,902
Held-to-Maturity Securities:
Amortized Cost				461,748
Amortized Cost, after Allowance for Credit Loss		452,955
Gross Unrealized Gains		169		270
Gross Unrealized Losses		(15,484)		(12,374)
Fair Value		438,113		450,042
Allowance for Credit Losses		(473)		(398)		$ 0
U.S. Government Bonds
Available-for-Sale Securities:
Amortized Cost		2,991		2,990
Gross Unrealized Losses		(211)		(206)
Fair Value		2,780		2,784
US Agency Bonds
Held-to-Maturity Securities:
Amortized Cost		25,000		25,000
Gross Unrealized Losses		(289)		(181)
Fair Value		24,711		24,819
Corporate Bonds
Available-for-Sale Securities:
Amortized Cost		25,782		25,790
Gross Unrealized Losses		(2,262)		(2,122)
Fair Value		23,520		23,668
Held-to-Maturity Securities:
Amortized Cost		82,500		82,500
Gross Unrealized Losses		(2,211)		(2,691)
Fair Value		80,289		79,809
Collateralized Mortgage Obligations
Available-for-Sale Securities:
Amortized Cost		38,183	[1]	39,375	[2]
Gross Unrealized Losses		(6,229)	[1]	(6,227)	[2]
Fair Value		31,954	[1]	33,148	[2]
Held-to-Maturity Securities:
Amortized Cost		207,079	[1]	212,093	[2]
Gross Unrealized Gains	[2]			104
Gross Unrealized Losses		(7,468)	[1]	(5,170)	[2]
Fair Value		199,611	[1]	207,027	[2]
FHLMC Certificates
Available-for-Sale Securities:
Amortized Cost		9,903		10,163
Gross Unrealized Losses		(1,424)		(1,482)
Fair Value		8,479		8,681
Held-to-Maturity Securities:
Amortized Cost		3,819		3,897
Gross Unrealized Losses		(253)		(244)
Fair Value		3,566		3,653
FNMA Certificates
Available-for-Sale Securities:
Amortized Cost		60,158		61,359
Gross Unrealized Losses		(10,948)		(9,842)
Fair Value		49,210		51,517
Held-to-Maturity Securities:
Amortized Cost		116,085		118,944
Gross Unrealized Losses		(5,263)		(4,088)
Fair Value		110,822		114,856
GNMA Certificates
Available-for-Sale Securities:
Amortized Cost		102		104
Gross Unrealized Losses		(1)
Fair Value		101		104
SBA Certificates
Held-to-Maturity Securities:
Amortized Cost		18,945		19,712
Gross Unrealized Gains		169		166
Fair Value		$ 19,114		$ 19,878

[1] Comprised of Federal Home Loan Mortgage Corporation (“FHLMC”), Federal National Mortgage Association (“FNMA”) and Ginnie Mae (“GNMA”) issued securities.

[2] Comprised of FHLMC, FNMA and GNMA issued securities.