Investment Securities (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) Security	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) Security	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) Security
Schedule Of Investments [Line Items]
Securities pledged as collateral	$ 891,000,000,000		$ 891,000,000,000		$ 845,200,000
Proceeds from Sale of Debt Securities, Available-for-Sale			$ 0	$ 0
Number of security positions, unrealized loss position | Security	189		189		201
Number of security positions, unrealized loss position for more than 12 months | Security	189		189		198
Securities, 12 months or longer, Fair Value	$ 871,635,000		$ 871,635,000		$ 835,522,000
Securities, 12 months or longer, Unrealized Losses	160,164,000		160,164,000		$ 151,546,000
Number of security positions, unrealized loss position for less than 12 months | Security					3
Securities, Less than 12 months, Fair Value	0		0		$ 8,000
Securities, Less than 12 months, Unrealized Losses	0		0		0
Available for sale securities, allowance for credit loss	0		0		0
Securities held to maturity, Amortized Cost	128,274,000		128,274,000		148,160,000
Internally rated held-to-maturity securities	$ 3,400,000		$ 3,400,000		$ 4,200,000
Investment, Type [Extensible Enumeration]	Municipal Bonds [Member]		Municipal Bonds [Member]		Municipal Bonds [Member]
Investment securities, past due	$ 4,461,468,000		$ 4,461,468,000		$ 4,462,139,000
Total Past Due [Member]
Schedule Of Investments [Line Items]
Investment securities, past due	16,044,000		16,044,000		29,347,000
Municipal Bonds [Member]
Schedule Of Investments [Line Items]
Securities held to maturity, Amortized Cost	49,400,000		49,400,000		64,600,000
Maximum [Member]
Schedule Of Investments [Line Items]
Securities, 12 months or longer, Unrealized Losses	160,200,000		160,200,000		151,500,000
Securities, Less than 12 months, Unrealized Losses					1,000
Available for Sale Securities [Member]
Schedule Of Investments [Line Items]
Accrued interest receivable	2,100,000		2,100,000
Held To Maturity Investment Securities [Member]
Schedule Of Investments [Line Items]
Accrued interest receivable	559,000		559,000		571,000
Held To Maturity Investment Securities [Member] | Total Past Due [Member]
Schedule Of Investments [Line Items]
Investment securities, past due	0		0		$ 0
Held To Maturity Investment Securities [Member] | Maximum [Member]
Schedule Of Investments [Line Items]
Provision for credit loss	$ 1,000	$ 1,000	$ 1,000	$ 1,000