v3.26.3
Investment Securities - Summary of Securities Available for Sale in an Unrealized Loss Position (Detail) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value $ 1,489,725 $ 172,626
Less than 12 months, Unrealized Losses 57,250 972
12 months or longer, Fair Value 1,675,716 1,998,999
12 months or longer, Unrealized Losses 264,751 215,667
Total, Fair Value 3,165,441 2,171,625
Total, Unrealized Losses 322,001 216,639
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 507 133
Less than 12 months, Unrealized Losses 6 1
12 months or longer, Fair Value 22,051 31,485
12 months or longer, Unrealized Losses 1,495 1,475
Total, Fair Value 22,558 31,618
Total, Unrealized Losses 1,501 1,476
State and Political Subdivisions [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 23,535 6,177
Less than 12 months, Unrealized Losses 2,237 543
12 months or longer, Fair Value 444,364 483,564
12 months or longer, Unrealized Losses 83,698 55,091
Total, Fair Value 467,899 489,741
Total, Unrealized Losses 85,935 55,634
Residential Mortgage-Backed Securities, Agency [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 1,373,378 109,848
Less than 12 months, Unrealized Losses 53,079 270
12 months or longer, Fair Value 675,737 795,183
12 months or longer, Unrealized Losses 141,881 114,047
Total, Fair Value 2,049,115 905,031
Total, Unrealized Losses 194,960 114,317
Residential Mortgage-Backed Securities, Non-agency [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 0 0
Less than 12 months, Unrealized Losses 0 0
12 months or longer, Fair Value 19,865 21,189
12 months or longer, Unrealized Losses 5,236 4,237
Total, Fair Value 19,865 21,189
Total, Unrealized Losses 5,236 4,237
Commercial Mortgage-Backed Securities Agency [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 84,294 6,287
Less than 12 months, Unrealized Losses 1,862 4
12 months or longer, Fair Value 212,641 293,038
12 months or longer, Unrealized Losses 21,532 26,048
Total, Fair Value 296,935 299,325
Total, Unrealized Losses 23,394 26,052
Asset-backed Securities [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 2,065 50,181
Less than 12 months, Unrealized Losses 15 154
12 months or longer, Fair Value 126,898 136,940
12 months or longer, Unrealized Losses 1,872 2,227
Total, Fair Value 128,963 187,121
Total, Unrealized Losses 1,887 2,381
Single Issue Trust Preferred Securities [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 0 0
Less than 12 months, Unrealized Losses 0 0
12 months or longer, Fair Value 12,984 12,658
12 months or longer, Unrealized Losses 353 661
Total, Fair Value 12,984 12,658
Total, Unrealized Losses 353 661
Other Corporate Securities [Member]    
Schedule of Investments [Line Items]    
Less than 12 months, Fair Value 5,946 0
Less than 12 months, Unrealized Losses 51 0
12 months or longer, Fair Value 161,176 224,942
12 months or longer, Unrealized Losses 8,684 11,881
Total, Fair Value 167,122 224,942
Total, Unrealized Losses $ 8,735 $ 11,881