SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to HTLF	$ 60,654	$ 56,564	$ 51,873	$ 43,089	$ 49,580	$ 55,924	$ 61,605	$ 52,814	$ 212,180	$ 219,923	$ 137,938
Preferred dividends	(2,012)	(2,013)	(2,012)	(2,013)	(2,012)	(2,013)	(2,012)	(2,013)	(8,050)	(8,050)	(4,451)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 58,642	$ 54,551	$ 49,861	$ 41,076	$ 47,568	$ 53,911	$ 59,593	$ 50,801	$ 204,130	$ 211,873	$ 133,487
Weighted average common shares outstanding for basic earnings per share (in shares)	42,578,977	42,574,557	42,474,835	42,359,582	42,309,003	42,302,780	42,242,893	42,174,092	42,496,000	42,260,000	37,269,000
Assumed incremental common shares issued upon exercise of stock options and non-vested restricted stock units (in shares)									135,000	151,000	88,000
Weighted average common shares for diluted earnings per share (in shares)	42,699,752	42,643,940	42,565,391	42,540,953	42,479,442	42,415,993	42,359,873	42,335,747	42,631,000	42,411,000	37,357,000
Earnings per common share — basic (in dollars per share)	$ 1.38	$ 1.28	$ 1.17	$ 0.97	$ 1.12	$ 1.27	$ 1.41	$ 1.20	$ 4.80	$ 5.01	$ 3.58
Earnings per common share — diluted (in dollars per share)	$ 1.37	$ 1.28	$ 1.17	$ 0.97	$ 1.12	$ 1.27	$ 1.41	$ 1.20	$ 4.79	$ 5.00	$ 3.57
Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of antidilutive stock units excluded from diluted earnings per share computation									5,000	1,000	0
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of antidilutive stock units excluded from diluted earnings per share computation									5,000	0	0