v3.26.1
Short-Term and Other Borrowings - Summary of Federal Funds Purchased, Securities Sold Under Agreements to Repurchase and Other Short-term Borrowings (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Short-term Debt [Line Items]      
Long-Term Subordinated Debentures, net of unamortized debt issuance costs $ 73,927   $ 73,885
Total Subordinated Debentures 104,276   104,234
First Citizens Statutory Trust II [Member]      
Short-term Debt [Line Items]      
Subordinated Debentures 7,732   7,732
First Citizens Statutory Trust III [Member]      
Short-term Debt [Line Items]      
Subordinated Debentures 12,887   12,887
First Citizens Statutory Trust IV [Member]      
Short-term Debt [Line Items]      
Subordinated Debentures 5,155   5,155
Futura TPF Trust I [Member]      
Short-term Debt [Line Items]      
Subordinated Debentures 2,578   2,578
Futura TPF Trust II [Member]      
Short-term Debt [Line Items]      
Subordinated Debentures 1,997   1,997
Federal Funds Purchased [Member]      
Short-term Debt [Line Items]      
Short-term borrowings 0   0
Short Term Borrowings, FHLB advances [Member]      
Short-term Debt [Line Items]      
Short-term borrowings 100,000   175,000
Maximum indebtedness $ 270,500 $ 394,000  
Maximum indebtedness, Rate 3.71% 4.42%  
End of period balance $ 100,000 $ 360,000  
End of period balance, Rate 3.82% 4.42%  
Average balance $ 148,656 $ 355,589  
Average rate paid 3.77% 4.42%  
Short Term Borrowings, FHLB advances [Member] | Single Maturity Fixed Rate Advances [Member]      
Short-term Debt [Line Items]      
Short-term borrowings $ 100,000   $ 100,000
Interest rate on balance 3.82%   3.81%
Short Term Borrowings, FHLB advances [Member] | Overnight [Member]      
Short-term Debt [Line Items]      
Short-term borrowings $ 0   $ 75,000
Interest rate on balance 0.00%   3.81%