Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Available-for-sale
Available-for-sale debt securities, less than 12 months, estimated fair value	$ 4,544,559
Available-for-sale debt securities, less than 12 months, gross unrealized losses	(42,797)
Available-for-sale debt securities, 12 months or more, estimated fair value	521,145
Available-for-sale debt securities, 12 months or more, gross unrealized losses	(18,524)
Available-for-sale debt securities, estimated fair value	5,065,704
Available-for-sale debt securities, gross unrealized losses	(61,321)
U.S. Government agencies
Available-for-sale
Available-for-sale debt securities, less than 12 months, estimated fair value	152,908
Available-for-sale debt securities, less than 12 months, gross unrealized losses	(3,297)
Available-for-sale debt securities, 12 months or more, estimated fair value	160,913
Available-for-sale debt securities, 12 months or more, gross unrealized losses	(7,311)
Available-for-sale debt securities, estimated fair value	313,821
Available-for-sale debt securities, gross unrealized losses	(10,608)
Mortgage-backed securities
Available-for-sale
Available-for-sale debt securities, less than 12 months, estimated fair value	3,632,822
Available-for-sale debt securities, less than 12 months, gross unrealized losses	(33,551)
Available-for-sale debt securities, 12 months or more, estimated fair value	323,683
Available-for-sale debt securities, 12 months or more, gross unrealized losses	(9,688)
Available-for-sale debt securities, estimated fair value	3,956,505
Available-for-sale debt securities, gross unrealized losses	(43,239)
State and political subdivisions
Available-for-sale
Available-for-sale debt securities, less than 12 months, estimated fair value	530,647
Available-for-sale debt securities, less than 12 months, gross unrealized losses	(709)
Available-for-sale debt securities, 12 months or more, estimated fair value	29,565
Available-for-sale debt securities, 12 months or more, gross unrealized losses	(1,286)
Available-for-sale debt securities, estimated fair value	560,212
Available-for-sale debt securities, gross unrealized losses	(1,995)
Other securities
Available-for-sale
Available-for-sale debt securities, less than 12 months, estimated fair value	228,182
Available-for-sale debt securities, less than 12 months, gross unrealized losses	(5,240)
Available-for-sale debt securities, 12 months or more, estimated fair value	6,984
Available-for-sale debt securities, 12 months or more, gross unrealized losses	(239)
Available-for-sale debt securities, estimated fair value	235,166
Available-for-sale debt securities, gross unrealized losses	$ (5,479)

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
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Amount of accumulated unrealized loss on 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 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

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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 less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on 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 less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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

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