Derivative Financial Instruments (Cash flow hedges) (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) transaction	Mar. 31, 2015 USD ($) transaction
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Change in net unrealized losses on cash flow hedges	$ 1.0
Estimated amount to be reclassified from accumulated other comprehensive income to interest expense within the next twelve months	$ 1.2
Interest Rate Swap | Heartland Financial Statutory Trust VI
Derivative [Line Items]
Number of swap transactions | transaction		2
Derivative, notional amount		$ 20.0
Interest Rate Swap | Cash Flow Hedges
Derivative [Line Items]
Number of swap transactions | transaction	5
Derivative, notional amount	$ 85.0
Interest Rate Swap | Cash Flow Hedges | Heartland Financial Statutory Trust IV, V and VII
Derivative [Line Items]
Derivative, notional amount	65.0
Interest Rate Swap | Cash Flow Hedges | Morrill Statutory Trust I and II
Derivative [Line Items]
Derivative, notional amount	$ 20.0