BASIS OF PRESENTATION (Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to HTLF	$ 64,153	$ 48,091	$ 155,602	$ 150,283
Preferred dividends	(2,013)	(2,013)	(6,038)	(6,038)
Net income available to common stockholders	$ 62,140	$ 46,078	$ 149,564	$ 144,245
Weighted average common shares outstanding for basic earnings per share (in shares)	43,000	42,761	42,908	42,681
Assumed incremental common shares issued upon vesting of outstanding restricted stock units (in shares)	195	52	172	89
Weighted average common shares for diluted earnings per share (in shares)	43,195	42,813	43,080	42,770
Earnings per common share — basic (in dollars per share)	$ 1.45	$ 1.08	$ 3.49	$ 3.38
Earnings per common share — diluted (in dollars per share)	$ 1.44	$ 1.08	$ 3.47	$ 3.37
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)	0	204	0	107
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)	31	58	53	62