BASIS OF PRESENTATION (Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to HTLF	$ 51,707	$ 52,776
Preferred dividends	(2,013)	(2,013)
Net income available to common stockholders	$ 49,694	$ 50,763
Weighted average common shares outstanding for basic earnings per share (in shares)	42,807	42,615
Assumed incremental common shares issued upon vesting of outstanding restricted stock units (in shares)	109	128
Weighted average common shares for diluted earnings per share (in shares)	42,916	42,743
Earnings per common share — basic (in dollars per share)	$ 1.16	$ 1.19
Earnings per common share — diluted (in dollars per share)	$ 1.16	$ 1.19
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)	27	50
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	61