Borrowings - Additional information (Details) $ in Thousands			1 Months Ended	3 Months Ended			6 Months Ended
	Feb. 24, 2023 USD ($)	Feb. 24, 2020 USD ($)	Dec. 31, 2016	Jun. 30, 2023 USD ($) item	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2023 USD ($) item	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Apr. 20, 2018 USD ($)
Borrowings
Securities available-for-sale, at fair value				$ 1,335,622			$ 1,335,622		$ 1,539,359
Number of customers having secured balances exceeding specified percentage of stockholders equity | item				0			0
Threshold percentage of stockholders' equity							10.00%
Borrowings at FHLBC as percentage of total assets				35.00%			35.00%
Borrowings at FHLBC as percentage of book value of certain mortgage loans				60.00%			60.00%
FHLBC stock				$ 21,800			$ 21,800		5,600
Federal Home Loan Bank Chicago ("FHLBC") and Federal Reserve Bank Chicago ("FRBC") stock				36,730			36,730		20,530
Proceeds from term note		$ 30,000
Repayment of term note							9,000	$ 2,000
Senior notes									44,585
Basis points added to reference rate (as a percent)		175.00%
Total borrowings				601,644			601,644		260,811
Asset Pledged as Collateral with Right | Securities sold under repurchase agreements
Borrowings
Investment securities pledged with financial institutions, dollars									32,200
Securities available-for-sale, at fair value				65,000			65,000		71,400
GCFC/ABC Bank
Borrowings
Debt assumed										$ 23,400
Balance of borrowings paid off					$ 5,900
Three Months Secured Overnight Financing Rate
Borrowings
Basis points added to reference rate (as a percent)						273.00%
Securities sold under repurchase agreements
Borrowings
Total borrowings				31,532			31,532		32,156
Securities sold under repurchase agreements | Asset Pledged as Collateral with Right | Securities sold under repurchase agreements
Borrowings
Investment securities pledged with financial institutions, dollars				$ 31,500			$ 31,500
Federal Home Loan Bank Advances
Borrowings
Borrowings at FHLBC as percentage of book value of certain mortgage loans				60.00%			60.00%
FHLBC advance amount				$ 485,000			$ 485,000		90,000
FHLBC stock				21,800			21,800
Principal balance of loans collateralized				1,480,000			1,480,000
Combined collateral value				1,040,000			1,040,000
Amount available for additional borrowings				551,300			551,300
Subordinated debentures
Borrowings
Total borrowings				59,339			59,339		59,297
Notes Payable to Banks [Member]
Borrowings
Total borrowings									9,000
Junior subordinated debentures
Borrowings
Total borrowings				$ 25,773			$ 25,773		$ 25,773
Senior Notes [Member]
Borrowings
Interest rate (as a percent)			5.75%
Debt Instrument, Term			10 years
Interest rate term			5 years
Effective interest rate				9.39%			9.39%		8.62%
Total borrowings									$ 44,585
Debt instrument redemption price, percentage				12.85%			100.00%
Debt redeemed amount				$ 45,000			$ 45,000
Debt issuance costs				362
Senior Notes [Member] | Debt Instrument Variable Rate Base LIBOR [Member]
Borrowings
Basis points added to reference rate (as a percent)			3.85%
Term Debt
Borrowings
Proceeds from term note		$ 20,000
Repayment of term note	$ 9,000
Debt term		3 years
Subordinated Notes Due 2031
Borrowings
Interest rate (as a percent)						3.50%
Outstanding, net of deferred issuance costs				$ 59,300			$ 59,300		$ 59,300
Face amount						$ 60,000