Other Borrowings (Trust Preferred Offerings) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 131,021
Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	5.56%
Heartland Financial Statutory Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 10,310
Interest rate (as a percent)	5.54%
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]
Trust preferred offerings outstanding	$ 20,619
Interest rate (as a percent)	3.77%
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]
Trust preferred offerings outstanding	$ 20,619
Interest rate (as a percent)	4.27%
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]
Trust preferred offerings outstanding	$ 20,619
Interest rate (as a percent)	4.22%
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]
Trust preferred offerings outstanding	$ 8,994
Interest rate (as a percent)	6.07%
Morrill Statutory Trust I | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.92%
Morrill Statutory Trust II | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 8,642
Interest rate (as a percent)	5.64%
Morrill Statutory Trust II | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.51%
Sheboygan Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 6,440
Interest rate (as a percent)	5.74%
CBNM Capital Trust I | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 4,359
Interest rate (as a percent)	6.04%
Citywide Capital Trust III | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 6,383
Interest rate (as a percent)	5.32%
Citywide Capital Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 4,238
Interest rate (as a percent)	4.85%
Citywide Capital Trust V | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 11,523
Interest rate (as a percent)	4.33%
OCGI Statutory Trust III | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 2,989
Interest rate (as a percent)	6.44%
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]
Trust preferred offerings outstanding	$ 5,286
Interest rate (as a percent)	5.29%
OCGI Capital Trust IV | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.37%
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%