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Securities - Amortized Cost and Fair Value (Details)	12 Months Ended
	Dec. 31, 2024 USD ($) item	Dec. 31, 2023 USD ($)
Securities Available-for-Sale
Amortized Cost	$ 1,230,328,000	$ 1,276,981,000
Gross Unrealized Gains	2,152,000	1,818,000
Gross Unrealized Losses	(70,779,000)	(85,970,000)
Securities available-for-sale	1,161,701,000	1,192,829,000
Accrued interest receivable	7,100,000	6,600,000
FHLB and FRB Stock
FHLBC stock	4,500,000	18,500,000
FRBC stock	14,900,000	14,900,000
Securities pledged to secure deposits and for other purposes	$ 717,500,000	810,200,000
Other disclosures
Number of securities issued from originators	0
Number of originators | item	1
Minimum percentage of securities investment	10.00%
US government and agencies debt securities, percentage of guarantee	100.00%
US government and agencies debt securities, threshold percentage of guarantee for allowance of credit loss	100.00%
U.S. Treasury
Securities Available-for-Sale
Amortized Cost	$ 193,902,000	174,602,000
Gross Unrealized Gains	700,000
Gross Unrealized Losses	(459,000)	(5,028,000)
Securities available-for-sale	194,143,000	169,574,000
U.S. government agencies
Securities Available-for-Sale
Amortized Cost	39,202,000	60,011,000
Gross Unrealized Losses	(1,388,000)	(3,052,000)
Securities available-for-sale	37,814,000	56,959,000
U.S. government agencies mortgage-backed
Securities Available-for-Sale
Amortized Cost	112,241,000	118,492,000
Gross Unrealized Losses	(11,964,000)	(12,122,000)
Securities available-for-sale	100,277,000	106,370,000
States and political subdivisions
Securities Available-for-Sale
Amortized Cost	226,969,000	236,072,000
Gross Unrealized Gains	264,000	1,325,000
Gross Unrealized Losses	(11,777,000)	(10,332,000)
Securities available-for-sale	215,456,000	227,065,000
Collateralized mortgage obligations
Securities Available-for-Sale
Amortized Cost	411,170,000	442,987,000
Gross Unrealized Gains	647,000	421,000
Gross Unrealized Losses	(43,201,000)	(50,864,000)
Securities available-for-sale	368,616,000	392,544,000
Asset-backed Securities
Securities Available-for-Sale
Amortized Cost	64,215,000	71,616,000
Gross Unrealized Gains	69,000	42,000
Gross Unrealized Losses	(1,981,000)	(3,222,000)
Securities available-for-sale	62,303,000	68,436,000
Collateralized loan obligations.
Securities Available-for-Sale
Amortized Cost	182,629,000	173,201,000
Gross Unrealized Gains	472,000	30,000
Gross Unrealized Losses	(9,000)	(1,350,000)
Securities available-for-sale	$ 183,092,000	$ 171,881,000
Minimum
Other disclosures
Debt securities, available-for-sale, allowance for credit loss, percent of market value loss	5.00%
Debt securities, available-for-sale, allowance for credit loss, market value loss	$ 200,000

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The market value loss of debt securities available for sale, for evaluation of allowance for credit loss.

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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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