Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 17,850,263	$ 13,445,888
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	56,001	518,805
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,124,579	40,065
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	16,781,685	13,924,628
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	4,656,896	2,165,702
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,093	23,333
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	242,690	9,602
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	4,416,299	2,179,433
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,967,803	4,059,692
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3,443	31,662
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	635,521	25,089
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	5,335,725	4,066,265
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	7,183,199	7,178,135
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	50,465	463,810
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	246,368	5,374
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	6,987,296	7,636,571
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,365	42,359
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	$ 42,365	$ 42,359

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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