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Securities - Schedule of Unrealized Losses on Investment Securities (Detail)
$ in Thousands
Sep. 30, 2025
USD ($)
Security
Dec. 31, 2024
USD ($)
Security
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 231,625 $ 223,438
Less than 12 months, Unrealized Losses $ (1,458) $ (1,966)
Less than 12 months, Number of Securities | Security 65 47
12 months or more, Fair Value $ 1,696,166 $ 1,850,875
12 months or more, Unrealized Losses $ (214,990) $ (293,453)
12 months or more, Number of Securities | Security 566 626
Fair Value, Total $ 1,927,791 $ 2,074,313
Unrealized Losses, Total $ (216,448) $ (295,419)
Number of Securities Total | Security 631 673
US Treasury Securities [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value   $ 48,846
Less than 12 months, Unrealized Losses   $ (63)
Less than 12 months, Number of Securities | Security   2
Fair Value, Total   $ 48,846
Unrealized Losses, Total   $ (63)
Number of Securities Total | Security   2
U.S. Government Sponsored Entities and Agencies [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 5,837  
Less than 12 months, Unrealized Losses $ (68)  
Less than 12 months, Number of Securities | Security 1  
12 months or more, Fair Value $ 191,084 $ 194,242
12 months or more, Unrealized Losses $ (21,912) $ (30,702)
12 months or more, Number of Securities | Security 42 43
Fair Value, Total $ 196,921 $ 194,242
Unrealized Losses, Total $ (21,980) $ (30,702)
Number of Securities Total | Security 43 43
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 168,195 $ 149,466
Less than 12 months, Unrealized Losses $ (1,086) $ (1,742)
Less than 12 months, Number of Securities | Security 39 32
12 months or more, Fair Value $ 1,351,860 $ 1,408,115
12 months or more, Unrealized Losses $ (187,806) $ (255,346)
12 months or more, Number of Securities | Security 441 447
Fair Value, Total $ 1,520,055 $ 1,557,581
Unrealized Losses, Total $ (188,892) $ (257,088)
Number of Securities Total | Security 480 479
Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 6,725 $ 9,919
Less than 12 months, Unrealized Losses $ (7) $ (7)
Less than 12 months, Number of Securities | Security 3 1
12 months or more, Fair Value $ 115,946 $ 193,085
12 months or more, Unrealized Losses $ (3,175) $ (4,135)
12 months or more, Number of Securities | Security 36 50
Fair Value, Total $ 122,671 $ 203,004
Unrealized Losses, Total $ (3,182) $ (4,142)
Number of Securities Total | Security 39 51
Asset-Backed Securities [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 35,661  
Less than 12 months, Unrealized Losses $ (143)  
Less than 12 months, Number of Securities | Security 9  
Fair Value, Total $ 35,661  
Unrealized Losses, Total $ (143)  
Number of Securities Total | Security 9  
Obligations of State and Political Subdivisions [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 2,657 $ 10,728
Less than 12 months, Unrealized Losses $ (121) $ (133)
Less than 12 months, Number of Securities | Security 4 8
12 months or more, Fair Value $ 31,803 $ 48,038
12 months or more, Unrealized Losses $ (2,087) $ (3,191)
12 months or more, Number of Securities | Security 45 84
Fair Value, Total $ 34,460 $ 58,766
Unrealized Losses, Total $ (2,208) $ (3,324)
Number of Securities Total | Security 49 92
Corporate Debt Securities [Member]    
Net Unrealized Gains And Losses On Investments [Line Items]    
Less than 12 months, Fair Value $ 12,550 $ 4,479
Less than 12 months, Unrealized Losses $ (33) $ (21)
Less than 12 months, Number of Securities | Security 9 4
12 months or more, Fair Value $ 5,473 $ 7,395
12 months or more, Unrealized Losses $ (10) $ (79)
12 months or more, Number of Securities | Security 2 2
Fair Value, Total $ 18,023 $ 11,874
Unrealized Losses, Total $ (43) $ (100)
Number of Securities Total | Security 11 6