Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 3,628,433	$ 2,639,241
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	48	13,048
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	396,790	184,424
Debt Securities, Held-to-maturity, Fair Value	3,231,691	2,467,865
Securities, held-to-maturity, allowance for credit loss	(310)	(158)
Securities held to maturity, net of allowance for credit losses of $310 at September 30, 2023 and $158 at December 31, 2022	3,628,123	2,639,083
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,258,155	526,122
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	113,142	65,322
Debt Securities, Held-to-maturity, Fair Value	1,145,013	460,800
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $310 at September 30, 2023 and $158 at December 31, 2022	1,258,155	526,122
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	2,368,778	2,111,619
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	48	13,048
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	283,585	119,033
Debt Securities, Held-to-maturity, Fair Value	2,085,241	2,005,634
Securities, held-to-maturity, allowance for credit loss	(310)	(158)
Securities held to maturity, net of allowance for credit losses of $310 at September 30, 2023 and $158 at December 31, 2022	2,368,468	2,111,461
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	63	69
Debt Securities, Held-to-maturity, Fair Value	1,437	1,431
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $310 at September 30, 2023 and $158 at December 31, 2022	$ 1,500	$ 1,500