Securities - Amortized Cost and Fair Value (Details) $ in Thousands	9 Months Ended
Sep. 30, 2026 USD ($) item security	Dec. 31, 2025 USD ($)
Securities Available-for-Sale
Amortized Cost	$ 1,043,824	$ 1,133,592
Gross Unrealized Gains	662	3,753
Gross Unrealized Losses	(65,910)	(46,822)
Fair Value	978,576	1,090,523
Accrued interest receivable	5,700	6,900
FHLB and FRB Stock
FHLBC stock	20,100	11,300
FRBC stock	$ 20,700	20,700
Other disclosures
Number of securities issued from originators \| security	0
Number of originators \| item	1
Minimum percentage of securities investment	10.00%
Securities pledged to secure deposits and for other purposes	$ 629,100	679,500
U.S. Treasury
Securities Available-for-Sale
Amortized Cost	149,225	164,296
Gross Unrealized Gains	54	1,564
Gross Unrealized Losses	(1,206)
Fair Value	148,073	165,860
U.S. government agencies
Securities Available-for-Sale
Amortized Cost	40,490	29,421
Gross Unrealized Losses	(1,381)	(245)
Fair Value	39,109	29,176
U.S. government agencies mortgage-backed
Securities Available-for-Sale
Amortized Cost	84,741	95,899
Gross Unrealized Losses	(9,906)	(7,119)
Fair Value	74,835	88,780
States and political subdivisions
Securities Available-for-Sale
Amortized Cost	190,475	213,366
Gross Unrealized Gains	3	450
Gross Unrealized Losses	(13,206)	(7,441)
Fair Value	177,272	206,375
Collateralized mortgage obligations
Securities Available-for-Sale
Amortized Cost	367,105	388,774
Gross Unrealized Gains	241	1,102
Gross Unrealized Losses	(38,556)	(30,571)
Fair Value	328,790	359,305
Asset-backed Securities
Securities Available-for-Sale
Amortized Cost	38,757	46,600
Gross Unrealized Gains	231	423
Gross Unrealized Losses	(1,593)	(1,207)
Fair Value	37,395	45,816
Collateralized loan obligations.
Securities Available-for-Sale
Amortized Cost	172,317	194,552
Gross Unrealized Gains	76	151
Gross Unrealized Losses	(62)	(239)
Fair Value	172,331	194,464
Equity Securities
Securities Available-for-Sale
Amortized Cost	714	684
Gross Unrealized Gains	57	63
Fair Value	$ 771	$ 747

Represents the minimum percentage of securities investment from originators.

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Represents the number of originators that the company has invested over 10 % of its stockholders equity.

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Represents the number of securities issued from originators.

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Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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