Other Borrowings (Trust Preferred Offerings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Less: deferred issuance costs	$ 90
Total	275,773	$ 274,905
Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	145,433
Total	$ 145,343	$ 130,913
Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.80%
Heartland Financial Statutory Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 10,310
Interest rate (as a percent)	4.65%
Heartland Financial Statutory Trust IV | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	5.01%
Heartland Financial Statutory Trust V | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 20,619
Interest rate (as a percent)	3.32%
Heartland Financial Statutory Trust V | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.69%
Heartland Financial Statutory Trust VI | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 20,619
Interest rate (as a percent)	3.37%
Heartland Financial Statutory Trust VI | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	3.87%
Heartland Financial Statutory Trust VII | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 18,042
Interest rate (as a percent)	3.39%
Heartland Financial Statutory Trust VII | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	3.83%
Morrill Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 9,088
Interest rate (as a percent)	5.20%
Morrill Statutory Trust II | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 8,754
Interest rate (as a percent)	4.75%
Sheboygan Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 6,528
Interest rate (as a percent)	4.85%
CBNM Capital Trust I | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 4,409
Interest rate (as a percent)	5.14%
Citywide Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 6,438
Interest rate (as a percent)	4.74%
Citywide Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 4,296
Interest rate (as a percent)	4.11%
Citywide Capital Trust V | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 11,748
Interest rate (as a percent)	3.43%
OCGI Statutory Trust III | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 2,996
Interest rate (as a percent)	5.48%
OCGI Statutory Trust III | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	5.53%
OCGI Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 5,342
Interest rate (as a percent)	4.39%
OCGI Capital Trust IV | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.37%
BVBC Capital Trust II | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 7,197
Interest rate (as a percent)	5.16%
BVBC Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Total trust preferred offerings	$ 9,047
Interest rate (as a percent)	3.54%
LIBOR | Heartland Financial Statutory Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.75%
LIBOR | Heartland Financial Statutory Trust V | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.33%
LIBOR | Heartland Financial Statutory Trust VI | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.48%
LIBOR | Heartland Financial Statutory Trust VII | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.48%
LIBOR | Morrill Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.25%
LIBOR | Morrill Statutory Trust II | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.85%
LIBOR | Sheboygan Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.95%
LIBOR | CBNM Capital Trust I | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.25%
LIBOR | Citywide Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.80%
LIBOR | Citywide Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.20%
LIBOR | Citywide Capital Trust V | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.54%
LIBOR | OCGI Statutory Trust III | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.65%
LIBOR | OCGI Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.50%
LIBOR | BVBC Capital Trust II | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.25%
LIBOR | BVBC Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.60%