Securities - Amortized Cost and Fair Value (Details) $ in Thousands	6 Months Ended
Jun. 30, 2024 USD ($) item	Dec. 31, 2023 USD ($)
Securities Available-for-Sale
Amortized Cost	$ 1,256,285	$ 1,276,981
Gross Unrealized Gains	1,138	1,818
Gross Unrealized Losses	(83,762)	(85,970)
Securities available-for-sale	1,173,661	1,192,829
Accrued interest receivable	6,700	6,600
FHLB and FRB Stock
FHLBC stock	17,100	18,500
FRBC stock	14,900	14,900
Securities pledged to secure deposits and for other purposes	762,200	810,200
Other disclosures
Securities available-for-sale	$ 1,173,661	1,192,829
Number of securities issued from originators \| item	0
Number of originators \| item	1
Minimum percentage of securities investment	10.00%
U.S. Treasury
Securities Available-for-Sale
Amortized Cost	$ 193,615	174,602
Gross Unrealized Gains	146
Gross Unrealized Losses	(2,487)	(5,028)
Securities available-for-sale	191,274	169,574
Other disclosures
Securities available-for-sale	191,274	169,574
U.S. government agencies
Securities Available-for-Sale
Amortized Cost	39,653	60,011
Gross Unrealized Losses	(2,355)	(3,052)
Securities available-for-sale	37,298	56,959
Other disclosures
Securities available-for-sale	37,298	56,959
U.S. government agencies mortgage-backed
Securities Available-for-Sale
Amortized Cost	109,490	118,492
Gross Unrealized Losses	(12,618)	(12,122)
Securities available-for-sale	96,872	106,370
Other disclosures
Securities available-for-sale	96,872	106,370
States and political subdivisions
Securities Available-for-Sale
Amortized Cost	232,373	236,072
Gross Unrealized Gains	470	1,325
Gross Unrealized Losses	(12,578)	(10,332)
Securities available-for-sale	220,265	227,065
Other disclosures
Securities available-for-sale	220,265	227,065
Collateralized mortgage obligations
Securities Available-for-Sale
Amortized Cost	436,623	442,987
Gross Unrealized Gains	321	421
Gross Unrealized Losses	(50,889)	(50,864)
Securities available-for-sale	386,055	392,544
Other disclosures
Securities available-for-sale	386,055	392,544
Asset-backed Securities
Securities Available-for-Sale
Amortized Cost	67,634	71,616
Gross Unrealized Gains	6	42
Gross Unrealized Losses	(2,763)	(3,222)
Securities available-for-sale	64,877	68,436
Other disclosures
Securities available-for-sale	64,877	68,436
Collateralized loan obligations.
Securities Available-for-Sale
Amortized Cost	176,897	173,201
Gross Unrealized Gains	195	30
Gross Unrealized Losses	(72)	(1,350)
Securities available-for-sale	177,020	171,881
Other disclosures
Securities available-for-sale	$ 177,020	$ 171,881

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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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