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Securities - Schedule of Changes in Equity Securities Without Readily Determinable Fair Values (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Equity Securities, FV-NI and without Readily Determinable Fair Value [Abstract]
Beginning balance	$ 533,749	$ 371,123	$ 416,750	$ 394,035
Acquisition of HTLF	(19,675)		103,211
Purchases of securities	34,919	33,397	83,749	45,154
Observable upward price adjustments	3,462	2,552	13,895	15,740
Observable downward price adjustments	(653)	(268)	(9,228)	(6,042)
Sales of securities and other activity	(10,783)	(7,032)	(67,358)	(49,115)
Ending balance	$ 541,019	$ 399,772	$ 541,019	$ 399,772

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- Definition

Equity securities without readily determinable fair value, acquisition of HTLF.

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- Definition

Equity securities without readily determinable fair value, purchases of securities.

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- Definition

Equity securities without readily determinable fair value, sales of securities and other activity.

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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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- Definition

Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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- Definition

Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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