Summary of Significant Accounting Policies (Earnings per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net income attributable to Heartland	$ 13,672	$ 21,632	$ 21,958	$ 18,010	$ 19,162	$ 20,208	$ 20,970	$ 20,009	$ 75,272	$ 80,349	$ 60,042
Preferred dividends	(13)	(13)	(13)	(19)	(19)	(53)	(52)	(168)	(58)	(292)	(817)
Interest expense on convertible preferred debt	0	3	4	5	3	17	31	0	12	51	0
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 13,659	$ 21,622	$ 21,949	$ 17,996	$ 19,146	$ 20,172	$ 20,949	$ 19,841	$ 75,226	$ 80,108	$ 59,225
Weighted average common shares outstanding for basic earnings per share (in shares)	29,948,536	29,647,534	26,686,845	26,334,788	25,498,423	24,601,016	24,524,273	23,657,234	28,168,000	24,573,000	20,672,000
Assumed incremental common shares issued upon exercise of stock options and non-vested restricted stock units (in shares)									258,000	300,000	257,000
Weighted average common shares for diluted earnings per share (in shares)	30,209,043	29,910,437	26,972,580	26,627,830	25,800,472	24,922,946	24,974,995	24,117,384	28,426,000	24,873,000	20,929,000
Earnings per common share — basic (in dollars per share)	$ 0.46	$ 0.73	$ 0.82	$ 0.68	$ 0.75	$ 0.82	$ 0.85	$ 0.84	$ 2.67	$ 3.26	$ 2.87
Earnings per common share — diluted (in dollars per share)	$ 0.45	$ 0.72	$ 0.81	$ 0.68	$ 0.74	$ 0.81	$ 0.84	$ 0.82	$ 2.65	$ 3.22	$ 2.83