Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Mar. 31, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 4,087,530
Available-for-sale, less than 12 months, gross unrealized losses	(251,450)
Available-for-sale, 12 months or more, estimated fair value	1,603,080
Available-for-sale, 12 months or more, gross unrealized losses	(184,476)
Available-for-sale, total, estimated fair value	5,690,610
Available-for-sale, total, gross unrealized losses	(435,926)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	94,352
Available-for-sale, less than 12 months, gross unrealized losses	(4,576)
Available-for-sale, 12 months or more, estimated fair value	211,178
Available-for-sale, 12 months or more, gross unrealized losses	(30,162)
Available-for-sale, total, estimated fair value	305,530
Available-for-sale, total, gross unrealized losses	(34,738)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	2,377,428
Available-for-sale, less than 12 months, gross unrealized losses	(115,730)
Available-for-sale, 12 months or more, estimated fair value	1,141,855
Available-for-sale, 12 months or more, gross unrealized losses	(96,789)
Available-for-sale, total, estimated fair value	3,519,283
Available-for-sale, total, gross unrealized losses	(212,519)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	1,337,236
Available-for-sale, less than 12 months, gross unrealized losses	(118,017)
Available-for-sale, 12 months or more, estimated fair value	152,722
Available-for-sale, 12 months or more, gross unrealized losses	(43,550)
Available-for-sale, total, estimated fair value	1,489,958
Available-for-sale, total, gross unrealized losses	(161,567)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	278,514
Available-for-sale, less than 12 months, gross unrealized losses	(13,127)
Available-for-sale, 12 months or more, estimated fair value	97,325
Available-for-sale, 12 months or more, gross unrealized losses	(13,975)
Available-for-sale, total, estimated fair value	375,839
Available-for-sale, total, gross unrealized losses	$ (27,102)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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