Fair Value (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable, Fair Value Disclosure	$ 7,264,580,000		$ 7,206,670,000
Alternative Investment	44,879,000		45,885,000
Loans Held-for-sale, Fair Value Disclosure	2,037,000		3,235,000
Impaired Financing Receivable, Carrying Value	$ 49,710,000		40,232,000
Discount percentage applied to real estate appraised values	15.00%
Discount percentage applied to lot development appraised values	6.00%
Partial Charge-Offs On Impaired Loans	$ 2,311,000		2,349,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	5,032,000		4,983,000
Impaired Loan Fair Value	1,817,000		2,497,000
Partial Charge-Offs On Impaired Loans carried at Fair Value	2,048,000		2,048,000
Book Value Of Impaired Loans Carried At Fair Value	1,852,000		2,499,000
Impaired Financing Receivable, carried at fair value, related expense	35,000	$ 107,000
MSR recorded at lower of cost or fair value	14,435,000	15,505,000	14,656,000	$ 15,792,000
Mortgage Servicing Rights Fair Value	1,000,000		900,000
Valuation allowance of MSR	69,000	168,000	94,000	$ 182,000
MSRs recorded at cost	13,400,000		13,800,000
Changes due to fair value adjustments	(25,000)	(14,000)
Other Real Estate, Foreclosed Assets, and Repossessed Assets	1,674,000		983,000
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	17,900,000		18,400,000
Alternative Investment, income recognized	690,000	378,000
Other Real Estate, Valuation Adjustments	0	$ 15,000
Fair Value Measured at Net Asset Value Per Share [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Alternative Investment	27,000,000		27,500,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable, Fair Value Disclosure	7,262,385,000		7,203,348,000
Impaired Loan Fair Value	1,817,000		2,497,000
Commercial Receivables, excluding Commercial, Financial, and Agricultural [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Related Allowance	35,000		2,000
Financing Receivable, not collateral dependent [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Related Allowance	4,997,000		4,981,000
Fair Value, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable, Fair Value Disclosure	1,817,000		2,497,000
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable, Fair Value Disclosure	1,817,000		2,497,000
Other Real Estate, Foreclosed Assets, and Repossessed Assets	$ 938,000		$ 938,000