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Borrowings - Additional information (Details)			3 Months Ended
Borrowings - Additional information (Details)	Apr. 06, 2021 USD ($)	Feb. 24, 2020 USD ($)	Mar. 31, 2022 USD ($) item	Dec. 31, 2016	Dec. 31, 2021 USD ($)	Apr. 20, 2018 USD ($)
Borrowings
Threshold percentage of stockholders' equity			10.00%
Borrowings at FHLBC as percentage of total assets			35.00%
Borrowings at FHLBC as percentage of book value of certain mortgage loans			60.00%
FHLBC stock			$ 7,100,000		$ 7,100,000
Federal Home Loan Bank Chicago ("FHLBC") and Federal Reserve Bank Chicago ("FRBC") stock			21,974,000		13,257,000
Proceeds from term note		$ 30,000,000.0
Senior notes			44,506,000		44,480,000
Basis points added to reference rate (as a percent)		175.00%
Total borrowings			181,025,000		198,876,000
GCFC/ABC Bank
Borrowings
FHLBC advance amount			$ 6,000,000.0
Debt assumed						$ 23,400,000
GCFC/ABC Bank \| Maximum
Borrowings
Interest rate (as a percent)			2.83%
Three Months Secured Overnight Financing Rate
Borrowings
Basis points added to reference rate (as a percent)	273.00%
Securities sold under repurchase agreements
Borrowings
Carrying amount of securities secured			$ 33,500,000		50,300,000
Fair value of the pledged collateral			$ 107,300,000		113,000,000.0
Number of customers having secured balances exceeding specified percentage of stockholders equity \| item			0
Total borrowings			$ 33,521,000		50,337,000
Federal Home Loan Bank Advances
Borrowings
Borrowings at FHLBC as percentage of book value of certain mortgage loans			60.00%
FHLBC advance amount			$ 0		0
FHLBC stock			7,100,000
Principal balance of loans collateralized			545,000,000.0
Combined collateral value			396,900,000
Amount available for additional borrowings			315,900,000
Subordinated debentures
Borrowings
Total borrowings			59,233,000		59,212,000
Notes payable and other borrowings
Borrowings
Total borrowings			17,992,000		19,074,000
Junior subordinated debentures
Borrowings
Total borrowings			25,773,000		25,773,000
Senior notes
Borrowings
Interest rate (as a percent)				5.75%
Senior notes			44,500,000		44,500,000
Debt Instrument, Term				10 years
Interest rate term				5 years
Debt issuance costs			$ 494,000		520,000
Amortization period for deferred financing costs			10 years
Total borrowings			$ 44,506,000		$ 44,480,000
Senior notes \| Debt Instrument, Variable Rate Base LIBOR [Member]
Borrowings
Basis points added to reference rate (as a percent)				385.00%
Term Debt
Borrowings
Proceeds from term note		$ 20,000,000.0	$ 12,000,000.0
Debt term		3 years
Subordinated Notes Due 2031
Borrowings
Interest rate (as a percent)	3.50%
Face amount	$ 60,000,000.0