Derivative Financial Instruments (Executed interest rate swap) (Details) - Derivative Financial Instruments $ in Millions	Mar. 31, 2017 USD ($) transaction	May 10, 2016 USD ($)	Mar. 31, 2015 USD ($) transaction	Apr. 05, 2011 USD ($)
Derivative [Line Items]
Derivative, notional amount		$ 40.0		$ 15.0
Heartland Financial Statutory Trust VI
Derivative [Line Items]
Derivative, notional amount			$ 20.0
Number of swap transactions | transaction			2
Cash Flow Hedges
Derivative [Line Items]
Derivative, notional amount	$ 85.0
Number of swap transactions | transaction	5
Cash Flow Hedges | Heartland Financial Statutory Trust IV, V and VII
Derivative [Line Items]
Derivative, notional amount	$ 65.0
Cash Flow Hedges | Morrill Statutory Trust I and II
Derivative [Line Items]
Derivative, notional amount	$ 20.0