Other Borrowings (Trust Preferred Offerings) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 115,381
Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.97%
Heartland Financial Statutory Trust IV | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 25,774
Basis spread on variable rate (as a percent)	2.75%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	3.74%
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
Basis spread on variable rate (as a percent)	1.33%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	2.21%
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
Stated interest rate (as a percent)	6.75%
Interest rate (as a percent)	6.75%
Heartland Financial Statutory Trust VI | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	1.48%
Heartland Financial Statutory Trust VII | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 20,619
Basis spread on variable rate (as a percent)	1.48%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	2.41%
Heartland Financial Statutory Trust VII | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative (as a percent)	4.70%
Morrill Statutory Trust I | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 8,806
Basis spread on variable rate (as a percent)	3.25%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	4.25%
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	$ 8,420
Basis spread on variable rate (as a percent)	2.85%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	3.84%
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	$ 6,265
Basis spread on variable rate (as a percent)	2.95%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	3.94%
CBNM Capital Trust I | Trust preferred securities
Debt Instrument [Line Items]
Trust preferred offerings outstanding	$ 4,259
Basis spread on variable rate (as a percent)	3.25%
Description of variable rate basis	LIBOR
Interest rate (as a percent)	4.21%