Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 19,105,977	$ 17,013,723
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	684	83,690
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,008,033	1,126,817
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	17,098,628	15,970,596
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	2,564,377	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	180,863	148,357
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	2,383,514	2,456,517
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	10,836,499	8,818,139
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	43	54,668
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,295,476	751,013
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	9,541,066	8,121,794
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,662,848	5,548,304
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	641	29,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	531,694	227,447
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	5,131,795	5,349,857
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,253	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	$ 42,253	$ 42,428