Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Mar. 31, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 661,971
Available-for-sale, less than 12 months, gross unrealized losses	(20,920)
Available-for-sale, 12 months or more, estimated fair value	3,020,877
Available-for-sale, 12 months or more, gross unrealized losses	(398,337)
Available-for-sale, total, estimated fair value	3,682,848
Available-for-sale, total, gross unrealized losses	(419,257)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	2,220
Available-for-sale, less than 12 months, gross unrealized losses	(44)
Available-for-sale, 12 months or more, estimated fair value	0
Available-for-sale, 12 months or more, gross unrealized losses	0
Available-for-sale, total, estimated fair value	2,220
Available-for-sale, total, gross unrealized losses	(44)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	85,993
Available-for-sale, less than 12 months, gross unrealized losses	(2,409)
Available-for-sale, 12 months or more, estimated fair value	80,154
Available-for-sale, 12 months or more, gross unrealized losses	(3,962)
Available-for-sale, total, estimated fair value	166,147
Available-for-sale, total, gross unrealized losses	(6,371)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	442,923
Available-for-sale, less than 12 months, gross unrealized losses	(7,396)
Available-for-sale, 12 months or more, estimated fair value	1,980,733
Available-for-sale, 12 months or more, gross unrealized losses	(223,846)
Available-for-sale, total, estimated fair value	2,423,656
Available-for-sale, total, gross unrealized losses	(231,242)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	47,760
Available-for-sale, less than 12 months, gross unrealized losses	(2,572)
Available-for-sale, 12 months or more, estimated fair value	813,859
Available-for-sale, 12 months or more, gross unrealized losses	(162,002)
Available-for-sale, total, estimated fair value	861,619
Available-for-sale, total, gross unrealized losses	(164,574)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	83,075
Available-for-sale, less than 12 months, gross unrealized losses	(8,499)
Available-for-sale, 12 months or more, estimated fair value	146,131
Available-for-sale, 12 months or more, gross unrealized losses	(8,527)
Available-for-sale, total, estimated fair value	229,206
Available-for-sale, total, gross unrealized losses	$ (17,026)

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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