v3.26.3
Securities - Schedule of Amortized Cost and Fair Value of AFS and HTM Securities by Contractual Maturity (Detail) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year $ 212,760  
Total available-for-sale debt securities at amortized cost, After 1 year through 5 years 207,696  
Total available-for-sale debt securities at amortized cost, After 5 years through 10 years 355,001  
Total available-for-sale debt securities, Amortized Cost, After 10 years 2,893,963  
Available-for-sale, Amortized Cost 3,669,420 $ 3,472,812
Total held-to-maturity debt securities at amortized cost, Within one year 15,236  
Total held-to-maturity debt securities at amortized cost, After 1 year through 5 years 303,660  
Total held-to-maturity debt securities at amortized cost, After 5 years through 10 years 554,532  
Total held-to-maturity debt securities at amortized cost, After 10 years 220,711  
Held-to-maturity, Amortized Cost 1,094,139 1,132,114
Total debt securities, Amortized Cost 4,763,559 4,604,926
Total available-for-sale debt securities, Fair value, Within one year 212,239  
Total available-for-sale debt securities, Fair value, After 1 year through 5 years 195,863  
Total available-for-sale debt securities, Fair value, After 5 years through 10 years 316,522  
Total available-for-sale debt securities, Fair value, After 10 years 2,629,068  
Total available-for-sale debt securities, Fair value 3,353,692 3,288,332
Total held-to-maturity debt securities, Fair value, Within one year 15,127  
Total held-to-maturity debt securities, Fair value, After 1 year through 5 years 282,984  
Total held-to-maturity debt securities, Fair value, After 5 years through 10 years 454,488  
Total held-to-maturity debt securities, Fair value, After 10 years 171,604  
Total held-to-maturity debt securities, Fair value 924,203 1,035,957
Total debt securities, Fair Value $ 4,277,895 4,324,289
Available-for-sale debt securities, Weighted-average yield, Within One Year 3.87%  
Available-for-sale debt securities, Weighted-average yield, After 1 Year through 5 Years 3.41%  
Available-for-sale debt securities, Weighted-average yield, After 5 Years through 10 Years 2.60%  
Available-for-sale debt securities, Weighted-average yield, After 10 Years 3.59%  
Available-for-sale debt securities, Total 3.50%  
Held-to-maturity debt securities, Weighted-average yield, Within One Year 3.86%  
Held-to-maturity debt securities, Weighted-average yield, After 1 Year through 5 Years 3.52%  
Held-to-maturity debt securities, Weighted-average yield, After 5 Years through 10 Years 2.79%  
Held-to-maturity debt securities, Weighted-average yield, After 10 Years 3.06%  
Held-to-maturity debt securities, Weighted-average yield, Total 3.06%  
U.S. Treasury [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year $ 197,154  
Available-for-sale, Amortized Cost 197,154 196,586
Total available-for-sale debt securities, Fair value 196,710 196,857
U.S. Government Sponsored Entities and Agencies [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year 2,001  
Total available-for-sale debt securities at amortized cost, After 1 year through 5 years 87,307  
Total available-for-sale debt securities at amortized cost, After 5 years through 10 years 43,129  
Total available-for-sale debt securities, Amortized Cost, After 10 years 92,951  
Available-for-sale, Amortized Cost 225,388 243,408
Total held-to-maturity debt securities at amortized cost, After 1 year through 5 years 1,001  
Total held-to-maturity debt securities at amortized cost, After 5 years through 10 years 1,025  
Held-to-maturity, Amortized Cost 2,026 2,341
Total available-for-sale debt securities, Fair value 197,728 222,997
Total held-to-maturity debt securities, Fair value 1,850 2,207
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year 35  
Total available-for-sale debt securities at amortized cost, After 1 year through 5 years 26,153  
Total available-for-sale debt securities at amortized cost, After 5 years through 10 years 287,312  
Total available-for-sale debt securities, Amortized Cost, After 10 years 2,693,463  
Available-for-sale, Amortized Cost 3,006,963 2,771,608
Total held-to-maturity debt securities at amortized cost, After 1 year through 5 years 1,865  
Total held-to-maturity debt securities at amortized cost, After 5 years through 10 years 4,731  
Total held-to-maturity debt securities at amortized cost, After 10 years 16,512  
Held-to-maturity, Amortized Cost 23,108 27,014
Total available-for-sale debt securities, Fair value 2,729,247 2,610,448
Total held-to-maturity debt securities, Fair value 20,854 25,469
Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year 2,029  
Total available-for-sale debt securities at amortized cost, After 1 year through 5 years 29,958  
Total available-for-sale debt securities at amortized cost, After 5 years through 10 years 3,889  
Total available-for-sale debt securities, Amortized Cost, After 10 years 20,392  
Available-for-sale, Amortized Cost 56,268 66,043
Total available-for-sale debt securities, Fair value 52,650 63,615
Asset Backed Securities [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities, Amortized Cost, After 10 years 63,743  
Available-for-sale, Amortized Cost 63,743 69,095
Total available-for-sale debt securities, Fair value 63,601 68,935
Obligations of State and Political Subdivisions [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year 2,046  
Total available-for-sale debt securities at amortized cost, After 1 year through 5 years 37,938  
Total available-for-sale debt securities at amortized cost, After 5 years through 10 years 16,924  
Total available-for-sale debt securities, Amortized Cost, After 10 years 23,414  
Available-for-sale, Amortized Cost 80,322 74,738
Total held-to-maturity debt securities at amortized cost, Within one year 15,236  
Total held-to-maturity debt securities at amortized cost, After 1 year through 5 years 298,819  
Total held-to-maturity debt securities at amortized cost, After 5 years through 10 years 548,776  
Total held-to-maturity debt securities at amortized cost, After 10 years 204,199  
Held-to-maturity, Amortized Cost 1,067,030 1,100,788
Total available-for-sale debt securities, Fair value 74,077 73,188
Total held-to-maturity debt securities, Fair value 899,533 1,006,238
Corporate Debt Securities [Member]    
Amortized Cost and Fair Value Debt Securities [Line Items]    
Total available-for-sale debt securities at amortized cost, Within one year 9,495  
Total available-for-sale debt securities at amortized cost, After 1 year through 5 years 26,340  
Total available-for-sale debt securities at amortized cost, After 5 years through 10 years 3,747  
Available-for-sale, Amortized Cost 39,582 51,334
Total held-to-maturity debt securities at amortized cost, After 1 year through 5 years 1,975  
Held-to-maturity, Amortized Cost 1,975 1,971
Total available-for-sale debt securities, Fair value 39,679 52,292
Total held-to-maturity debt securities, Fair value $ 1,966 $ 2,043