Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 3,601,039	$ 3,619,738
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	20,197	43,066
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	169,920	130,760
Debt Securities, Held-to-maturity, Fair Value	3,451,316	3,532,044
Securities, held-to-maturity, allowance for credit loss	(310)	(310)
Securities held to maturity, net of allowance for credit losses of $310 at both March 31, 2024 and December 31, 2023	3,600,729	3,619,428
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,239,420	1,250,431
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	76
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	69,069	54,175
Debt Securities, Held-to-maturity, Fair Value	1,170,351	1,196,332
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $310 at both March 31, 2024 and December 31, 2023	1,239,420	1,250,431
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	2,360,119	2,367,807
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	20,197	42,990
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	100,817	76,540
Debt Securities, Held-to-maturity, Fair Value	2,279,499	2,334,257
Securities, held-to-maturity, allowance for credit loss	(310)	(310)
Securities held to maturity, net of allowance for credit losses of $310 at both March 31, 2024 and December 31, 2023	2,359,809	2,367,497
Other Investments [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,500	1,500
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	34	45
Debt Securities, Held-to-maturity, Fair Value	1,466	1,455
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $310 at both March 31, 2024 and December 31, 2023	$ 1,500	$ 1,500