Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 19,144,541	$ 17,013,723
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	83,923	83,690
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,138,491	1,126,817
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	18,089,973	15,970,596
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,080,180	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	154,229	148,357
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	2,925,951	2,456,517
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	10,558,944	8,818,139
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	41,866	54,668
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	781,500	751,013
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	9,819,310	8,121,794
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,462,850	5,548,304
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	42,057	29,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	202,762	227,447
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	5,302,145	5,349,857
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,567	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	$ 42,567	$ 42,428