Borrowed Funds - Additional Information (Detail) $ in Thousands		1 Months Ended		3 Months Ended
	Jan. 31, 2025 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2025 USD ($) LettersOfCredit	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Long-term debt				$ 654,380	$ 385,292
Retired subordinated notes				11,055
FHLB Stock owned				$ 10,500	10,200
Federal Home Loan Bank 5.04% and 5.04% [Member]
Debt Instrument [Line Items]
Number of letters of credit outstanding | LettersOfCredit				30
Letter of Credit | Federal Home Loan Bank 5.04% and 5.04% [Member]
Debt Instrument [Line Items]
Letter of credit				$ 409,200
Letter of credit, expiration date				Jul. 31, 2025
Borrowing capacity				$ 1,600,000
Subordinated notes 3.70%, net of issuance costs [Member]
Debt Instrument [Line Items]
Subordinated notes, issued			$ 200,000
Debt instrument, interest rate			3.70%
Debt instrument, maturity date			Sep. 17, 2030
Debt instrument, frequency of periodic payment				semi-annually
Debt instrument, redemption, description				The Company may redeem the notes, in whole or in part, on September 17, 2025, or on any interest payment date thereafter.
Debt instrument, redemption period, start date			Sep. 17, 2025
Unamortized debt issuance costs				$ 200	300
Retired subordinated notes				$ 11,100
Subordinated notes 6.25%, net of issuance costs [Member]
Debt Instrument [Line Items]
Subordinated notes, issued		$ 110,000
Debt instrument, interest rate		6.25%
Debt instrument, maturity date		Sep. 28, 2032
Debt instrument, frequency of periodic payment				semi-annually
Debt instrument, redemption, description				The Company may redeem the notes, in whole or in part, on September 28, 2027, or on any interest payment date thereafter.
Debt instrument, redemption period, start date		Sep. 28, 2027
Unamortized debt issuance costs				$ 1,100	1,200
Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Long-term debt				$ 216,826	76,782
Heartland Financial USA, Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 278,018
Heartland Financial USA, Inc [Member] | Subordinated notes 2.75% [Member]
Debt Instrument [Line Items]
Subordinated notes, issued	$ 150,000
Debt instrument, interest rate	2.75%
Debt instrument, maturity date	Sep. 15, 2031
Debt instrument, frequency of periodic payment				semi-annually
Debt instrument, redemption, description				The Company may redeem the notes, in whole or in part, on September 15, 2026, or on any interest payment date thereafter.
Fair value of subordinated notes	$ 138,800
Marquette Capital Trust I, Marquette Capital Trust II, Marquette Capital Trust III And Marquette Capital Trust IV [Member] | Marquette [Member]
Debt Instrument [Line Items]
Long-term debt					103,100
Long-term debt acquired at fair value					$ 76,800
Marquette Financial Companies and HTLF [Member] | Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Long-term debt obligations aggregate contractual balance				$ 262,900
Long-term debt				$ 216,800