Summary of Significant Accounting Policies (Earnings per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net income attributable to Heartland	$ 32,141	$ 33,710	$ 27,879	$ 23,268	$ 13,672	$ 21,632	$ 21,958	$ 18,010	$ 116,998	$ 75,272	$ 80,349
Preferred dividends	0	(13)	(13)	(13)	(13)	(13)	(13)	(19)	(39)	(58)	(292)
Interest expense on convertible preferred debt					0	3	4	5	0	12	51
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 32,141	$ 33,697	$ 27,866	$ 23,255	$ 13,659	$ 21,622	$ 21,949	$ 17,996	$ 116,959	$ 75,226	$ 80,108
Weighted average common shares outstanding for basic earnings per share (in shares)	34,474,336	34,452,377	32,620,775	30,441,776	29,948,536	29,647,534	26,686,845	26,334,788	33,012,000	28,168,000	24,573,000
Assumed incremental common shares issued upon exercise of stock options and non-vested restricted stock units (in shares)									201,000	258,000	300,000
Weighted average common shares for diluted earnings per share (in shares)	34,670,180	34,644,187	32,830,751	30,645,212	30,209,043	29,910,437	26,972,580	26,627,830	33,213,000	28,426,000	24,873,000
Earnings per common share — basic (in dollars per share)	$ 0.93	$ 0.98	$ 0.85	$ 0.76	$ 0.46	$ 0.73	$ 0.82	$ 0.68	$ 3.54	$ 2.67	$ 3.26
Earnings per common share — diluted (in dollars per share)	$ 0.93	$ 0.97	$ 0.85	$ 0.76	$ 0.45	$ 0.72	$ 0.81	$ 0.68	$ 3.52	$ 2.65	$ 3.22