Derivative Financial Instruments (Executed Interest Rate Swap) (Details) $ in Millions	Dec. 31, 2016 USD ($) transaction	May 10, 2016 USD ($)	Mar. 31, 2015 USD ($) transaction	Apr. 20, 2011 USD ($)
Interest Rate Swap
Derivative [Line Items]
Derivative, notional amount				$ 15.0
Forward-starting Interest Rate Swap | Cash Flow Hedging
Derivative [Line Items]
Number of interest rate swap transactions | transaction	5
Interest Rate Swap
Derivative [Line Items]
Derivative, notional amount		$ 40.0
Interest Rate Swap | Heartland Financial Statutory Trust VI
Derivative [Line Items]
Derivative, notional amount			$ 20.0
Number of interest rate swap transactions | transaction			2
Interest Rate Swap | Cash Flow Hedging
Derivative [Line Items]
Derivative, notional amount	$ 85.0
Number of interest rate swap transactions | transaction	5
Interest Rate Swap | Cash Flow Hedging | Heartland Financial Statutory Trust IV, V and VII
Derivative [Line Items]
Derivative, notional amount	$ 65.0
Interest Rate Swap | Cash Flow Hedging | Morrill Statutory Trust I and II
Derivative [Line Items]
Derivative, notional amount	$ 20.0