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Securities - Schedule of Changes in Equity Securities Without Readily Determinable Fair Values (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Equity Securities, FV-NI and without Readily Determinable Fair Value [Abstract]
Beginning balance	$ 524,112	$ 416,750
Acquisition of HTLF		121,769
Purchases of securities	33,664	24,003
Observable upward price adjustments	3,568	1,022
Observable downward price adjustments	(636)	(6,273)
Sales of securities and other activity	(25,382)	(17,341)
Ending balance	$ 535,326	$ 539,930

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- Definition

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

+ References

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- Definition

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

+ References

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- Definition

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

+ References

No definition available.

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- References

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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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