v3.26.1
Borrowed Funds - Summary of Outstanding Trust Preferred Securities (Detail) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Debt Instrument [Line Items]    
Amount Outstanding $ 480,126 $ 474,229
Trust Preferred Securities [Member]    
Debt Instrument [Line Items]    
Amount Outstanding 222,345 $ 220,034
Trust Preferred Securities [Member] | Marquette Capital Trust I [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 19,517  
Issuance Date Dec. 28, 2005  
Interest Rate 1.33% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.26%  
Maturity Date Jan. 07, 2036  
Trust Preferred Securities [Member] | Marquette Capital Trust II [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 19,974  
Issuance Date Dec. 28, 2005  
Interest Rate 1.33% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.26%  
Maturity Date Jan. 07, 2036  
Trust Preferred Securities [Member] | Marquette Capital Trust III [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 7,841  
Issuance Date May 30, 2006  
Interest Rate 1.50% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.46%  
Maturity Date Jun. 23, 2036  
Trust Preferred Securities [Member] | Marquette Capital Trust IV [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 31,616  
Issuance Date Jun. 30, 2006  
Interest Rate 1.60% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.53%  
Maturity Date Sep. 15, 2036  
Trust Preferred Securities [Member] | Heartland Financial Statutory Trust IV [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 9,755  
Issuance Date Mar. 17, 2004  
Interest Rate 2.75% over 3-month term SOFR  
Interest Rate as of June 30, 2026 6.68%  
Maturity Date Mar. 17, 2034  
Trust Preferred Securities [Member] | Heartland Financial Statutory Trust V [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 17,717  
Issuance Date Jan. 27, 2006  
Interest Rate 1.33% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.26%  
Maturity Date Apr. 07, 2036  
Trust Preferred Securities [Member] | Heartland Financial Statutory Trust VI [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 17,153  
Issuance Date Jun. 21, 2007  
Interest Rate 1.48% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.41%  
Maturity Date Sep. 15, 2037  
Trust Preferred Securities [Member] | Heartland Financial Statutory Trust VII [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 15,008  
Issuance Date Jun. 26, 2007  
Interest Rate 1.48% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.40%  
Maturity Date Sep. 01, 2037  
Trust Preferred Securities [Member] | Morrill Statutory Trust I [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 10,054  
Issuance Date Dec. 19, 2002  
Interest Rate 3.25% over 3-month term SOFR  
Interest Rate as of June 30, 2026 7.26%  
Maturity Date Dec. 26, 2032  
Trust Preferred Securities [Member] | Morrill Statutory Trust II [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 9,819  
Issuance Date Dec. 17, 2003  
Interest Rate 2.85% over 3-month term SOFR  
Interest Rate as of June 30, 2026 6.78%  
Maturity Date Dec. 17, 2033  
Trust Preferred Securities [Member] | Sheboygan Statutory Trust I [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 7,411  
Issuance Date Sep. 17, 2003  
Interest Rate 2.95% over 3-month term SOFR  
Interest Rate as of June 30, 2026 6.88%  
Maturity Date Sep. 17, 2033  
Trust Preferred Securities [Member] | CBNM Capital Trust I [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 4,883  
Issuance Date Sep. 10, 2004  
Interest Rate 3.25% over 3-month term SOFR  
Interest Rate as of June 30, 2026 7.18%  
Maturity Date Dec. 15, 2034  
Trust Preferred Securities [Member] | Citywide Capital Trust III [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 6,861  
Issuance Date Dec. 19, 2003  
Interest Rate 2.80% over 3-month term SOFR  
Interest Rate as of June 30, 2026 6.73%  
Maturity Date Dec. 19, 2033  
Trust Preferred Securities [Member] | Citywide Capital Trust IV [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 4,749  
Issuance Date Sep. 30, 2004  
Interest Rate 2.20% over 3-month term SOFR  
Interest Rate as of June 30, 2026 6.10%  
Maturity Date Sep. 30, 2034  
Trust Preferred Securities [Member] | Citywide Capital Trust V [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 13,282  
Issuance Date May 31, 2006  
Interest Rate 1.54% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.47%  
Maturity Date Jul. 25, 2036  
Trust Preferred Securities [Member] | OCGI Statutory Trust III [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 3,040  
Issuance Date Jun. 27, 2002  
Interest Rate 3.65% over 3-month term SOFR  
Interest Rate as of June 30, 2026 7.58%  
Maturity Date Sep. 30, 2032  
Trust Preferred Securities [Member] | OCGI Statutory Trust IV [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 5,722  
Issuance Date Sep. 23, 2004  
Interest Rate 2.50% over 3-month term SOFR  
Interest Rate as of June 30, 2026 6.43%  
Maturity Date Dec. 15, 2034  
Trust Preferred Securities [Member] | BVBC Capital Trust II [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 7,506  
Issuance Date Apr. 10, 2003  
Interest Rate 3.25% over 3-month term SOFR  
Interest Rate as of June 30, 2026 7.17%  
Maturity Date Apr. 24, 2033  
Trust Preferred Securities [Member] | BVBC Capital Trust III [Member]    
Debt Instrument [Line Items]    
Amount Outstanding $ 10,437  
Issuance Date Jul. 29, 2005  
Interest Rate 1.60% over 3-month term SOFR  
Interest Rate as of June 30, 2026 5.59%  
Maturity Date Sep. 30, 2035