Securities - Amortized Cost and Fair Value (Details) $ in Thousands	9 Months Ended
Sep. 30, 2022 USD ($) item	Dec. 31, 2021 USD ($)
Securities Available-for-Sale
Amortized Cost	$ 1,740,730	$ 1,678,160
Gross Unrealized Gains	29	20,587
Gross Unrealized Losses	(131,000)	(5,115)
Securities available-for-sale	1,609,759	1,693,632
Accrued interest receivable	6,300	4,300
FHLB and FRB Stock
FHLBC stock	4,500	7,100
FRBC stock	14,900	6,200
Securities pledged to secure deposits and for other purposes	578,500	501,300
Other disclosures
Securities available-for-sale	1,609,759	1,693,632
Total added credit enhancement in the form of overcollaterization and/or subordination of outstanding principal	$ 20,300
Percentage of total added credit enhancement in the form of overcollaterization and/or subordination of outstanding principal	9.29
Number of securities issued from originators \| item	0
Minimum percentage of securities investment	10.00%
Reimbursement requests greater than 5 %
Other disclosures
Percentage of outstanding principal amount of loans guaranteed by US Department of Education	85
Percent of insured loan	5
Reimbursement requests greater than 9 %
Other disclosures
Percentage of outstanding principal amount of loans guaranteed by US Department of Education	75
Percent of insured loan	9
U.S. Treasury
Securities Available-for-Sale
Amortized Cost	$ 223,910	202,251
Gross Unrealized Gains		125
Gross Unrealized Losses	(12,813)	(37)
Securities available-for-sale	211,097	202,339
Other disclosures
Securities available-for-sale	211,097	202,339
U.S. government agencies
Securities Available-for-Sale
Amortized Cost	61,364	62,587
Gross Unrealized Losses	(5,401)	(699)
Securities available-for-sale	55,963	61,888
Other disclosures
Securities available-for-sale	55,963	61,888
U.S. government agencies mortgage-backed
Securities Available-for-Sale
Amortized Cost	145,857	172,016
Gross Unrealized Gains		856
Gross Unrealized Losses	(18,231)	(570)
Securities available-for-sale	127,626	172,302
Other disclosures
Securities available-for-sale	127,626	172,302
States and political subdivisions
Securities Available-for-Sale
Amortized Cost	243,515	241,937
Gross Unrealized Gains	1	16,344
Gross Unrealized Losses	(19,257)	(672)
Securities available-for-sale	224,259	257,609
Other disclosures
Securities available-for-sale	224,259	257,609
Corporate bonds
Securities Available-for-Sale
Amortized Cost	10,000	10,000
Gross Unrealized Losses	(456)	(113)
Securities available-for-sale	9,544	9,887
Other disclosures
Securities available-for-sale	9,544	9,887
Collateralized mortgage obligations
Securities Available-for-Sale
Amortized Cost	648,044	673,238
Gross Unrealized Gains	5	2,014
Gross Unrealized Losses	(60,203)	(2,285)
Securities available-for-sale	587,846	672,967
Other disclosures
Securities available-for-sale	587,846	672,967
Asset-backed Securities
Securities Available-for-Sale
Amortized Cost	227,130	236,293
Gross Unrealized Gains	23	1,245
Gross Unrealized Losses	(7,566)	(661)
Securities available-for-sale	219,587	236,877
Other disclosures
Securities available-for-sale	219,587	236,877
FFEL
Securities Available-for-Sale
Securities available-for-sale	167,000
Other disclosures
Securities available-for-sale	$ 167,000
Percentage of outstanding principal amount of loans guaranteed by US Department of Education	97
Collateralized loan obligations.
Securities Available-for-Sale
Amortized Cost	$ 180,910	79,838
Gross Unrealized Gains		3
Gross Unrealized Losses	(7,073)	(78)
Securities available-for-sale	173,837	79,763
Other disclosures
Securities available-for-sale	$ 173,837	$ 79,763

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Represents the percent of insured loans used as base for loans guaranteed by US Department of Education.

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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 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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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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