Investment Securities, Securities Held-to-Maturity (Details) - USD ($) $ in Thousands		Sep. 30, 2023		Dec. 31, 2022		Dec. 31, 2021
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost		$ 826,015		$ 845,346
Gross unrealized gains		1		78
Gross unrealized losses		189,393		157,031
Fair value		636,623		688,393
Allowance for credit losses		450		393		$ 393
Mortgage-backed Securities [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost	[1]	673,924		702,858
Gross unrealized gains	[1]	0		29
Gross unrealized losses	[1]	170,743		141,121
Fair value	[1]	503,181		561,766
Allowance for credit losses		0	[1]	0	[1]	0
Collateralized Mortgage Obligations [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost	[1]	75,507		80,186
Gross unrealized gains	[1]	0		0
Gross unrealized losses	[1]	17,676		15,701
Fair value	[1]	57,831		64,485
Allowance for credit losses		0	[1]	0	[1]	0
Municipal Securities [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost		76,584		62,302
Gross unrealized gains		1		49
Gross unrealized losses		974		209
Fair value		75,611		62,142
Allowance for credit losses		$ 450		$ 393		$ 393

[1] All mortgage-backed securities and collateralized mortgage obligations were issued by an agency or government sponsored entity of the U.S. Government.