TERM DEBT (Trust Preferred Offerings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term debt	$ 372,396	$ 371,753
Trust preferred securities
Debt Instrument [Line Items]
Long-term debt	149,288	$ 148,284
Heartland Financial Statutory Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 10,310
Interest rate (as a percent)	8.39%
Heartland Financial Statutory Trust V | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 20,619
Interest rate (as a percent)	6.99%
Heartland Financial Statutory Trust VI | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 20,619
Interest rate (as a percent)	7.13%
Heartland Financial Statutory Trust VII | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 18,042
Interest rate (as a percent)	7.12%
Morrill Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 9,464
Interest rate (as a percent)	8.87%
Morrill Statutory Trust II | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 9,198
Interest rate (as a percent)	8.49%
Sheboygan Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 6,878
Interest rate (as a percent)	8.59%
CBNM Capital Trust I | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 4,608
Interest rate (as a percent)	8.90%
Citywide Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 6,661
Interest rate (as a percent)	8.45%
Citywide Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 4,526
Interest rate (as a percent)	7.84%
Citywide Capital Trust V | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 12,649
Interest rate (as a percent)	7.19%
OCGI Statutory Trust III | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 3,028
Interest rate (as a percent)	9.31%
OCGI Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 5,567
Interest rate (as a percent)	8.15%
BVBC Capital Trust II | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 7,359
Interest rate (as a percent)	8.89%
BVBC Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 9,760
Interest rate (as a percent)	7.19%
Secured Overnight Financing Rate (SOFR) | Heartland Financial Statutory Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.75%
Secured Overnight Financing Rate (SOFR) | Heartland Financial Statutory Trust V | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.33%
Secured Overnight Financing Rate (SOFR) | Heartland Financial Statutory Trust VI | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.48%
Secured Overnight Financing Rate (SOFR) | Heartland Financial Statutory Trust VII | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.48%
Secured Overnight Financing Rate (SOFR) | Morrill Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.25%
Secured Overnight Financing Rate (SOFR) | Morrill Statutory Trust II | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.85%
Secured Overnight Financing Rate (SOFR) | Sheboygan Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.95%
Secured Overnight Financing Rate (SOFR) | CBNM Capital Trust I | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.25%
Secured Overnight Financing Rate (SOFR) | Citywide Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.80%
Secured Overnight Financing Rate (SOFR) | Citywide Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.20%
Secured Overnight Financing Rate (SOFR) | Citywide Capital Trust V | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.54%
Secured Overnight Financing Rate (SOFR) | OCGI Statutory Trust III | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.65%
Secured Overnight Financing Rate (SOFR) | OCGI Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.50%
Secured Overnight Financing Rate (SOFR) | BVBC Capital Trust II | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.25%
Secured Overnight Financing Rate (SOFR) | BVBC Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.60%