Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 17,935,916	$ 17,013,723
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	51,251	83,690
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,196,561	1,126,817
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	16,790,606	15,970,596
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,444,981	2,604,852
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	22
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	153,427	148,357
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	3,291,554	2,456,517
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	9,021,077	8,818,139
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	35,936	54,668
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	776,782	751,013
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	8,280,231	8,121,794
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,427,357	5,548,304
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	15,315	29,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	266,352	227,447
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	5,176,320	5,349,857
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,501	42,428
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	$ 42,501	$ 42,428