BASIS OF PRESENTATION (Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to HTLF	$ 39,742	$ 49,416	$ 91,449	$ 102,192
Preferred dividends	(2,012)	(2,012)	(4,025)	(4,025)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 37,730	$ 47,404	$ 87,424	$ 98,167
Weighted average common shares outstanding for basic earnings per share (in shares)	42,918	42,696	42,862	42,655
Assumed incremental common shares issued upon vesting of outstanding restricted stock units (in shares)	142	62	139	98
Weighted average common shares for diluted earnings per share (in shares)	43,060	42,758	43,001	42,753
Earnings per common share — basic (in dollars per share)	$ 0.88	$ 1.11	$ 2.03	$ 2.30
Earnings per common share — diluted (in dollars per share)	$ 0.88	$ 1.11	$ 2.03	$ 2.30
Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of antidilutive common stock equivalents and stock options excluded from diluted earnings per share computation (in shares)	88	59	6	95
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of antidilutive common stock equivalents and stock options excluded from diluted earnings per share computation (in shares)	53	221	53	62