Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net income attributable to Heartland	$ 37,851	$ 34,612	$ 45,169	$ 31,497	$ 32,141	$ 33,710	$ 27,879	$ 23,268	$ 149,129	$ 116,998	$ 75,272
Preferred dividends					0	(13)	(13)	(13)	0	(39)	(58)
Interest expense on convertible preferred debt									0	0	12
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 37,851	$ 34,612	$ 45,169	$ 31,497	$ 32,141	$ 33,697	$ 27,866	$ 23,255	$ 149,129	$ 116,959	$ 75,226
Weighted average common shares outstanding for basic earnings per share (in shares)	36,758,025	36,692,381	35,743,986	34,564,378	34,474,336	34,452,377	32,620,775	30,441,776	35,991,000	33,012,000	28,168,000
Assumed incremental common shares issued upon exercise of stock options and non-vested restricted stock units (in shares)									71,000	201,000	258,000
Weighted average common shares for diluted earnings per share (in shares)	36,840,519	36,835,191	35,879,259	34,699,839	34,670,180	34,644,187	32,830,751	30,645,212	36,062,000	33,213,000	28,426,000
Earnings per common share — basic (in dollars per share)	$ 1.03	$ 0.94	$ 1.26	$ 0.91	$ 0.93	$ 0.98	$ 0.85	$ 0.76	$ 4.14	$ 3.54	$ 2.67
Earnings per common share — diluted (in dollars per share)	$ 1.03	$ 0.94	$ 1.26	$ 0.91	$ 0.93	$ 0.97	$ 0.85	$ 0.76	$ 4.14	$ 3.52	$ 2.65