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 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Short-term Debt [Line Items]          
Long-Term Subordinated Debentures, net of unamortized debt issuance costs $ 73,968   $ 73,968   $ 73,885
Total Subordinated Debentures 104,317   104,317   104,234
First Citizens Statutory Trust II [Member]          
Short-term Debt [Line Items]          
Subordinated Debentures 7,732   7,732   7,732
First Citizens Statutory Trust III [Member]          
Short-term Debt [Line Items]          
Subordinated Debentures 12,887   12,887   12,887
First Citizens Statutory Trust IV [Member]          
Short-term Debt [Line Items]          
Subordinated Debentures 5,155   5,155   5,155
Futura TPF Trust I [Member]          
Short-term Debt [Line Items]          
Subordinated Debentures 2,578   2,578   2,578
Futura TPF Trust II [Member]          
Short-term Debt [Line Items]          
Subordinated Debentures 1,997   1,997   1,997
Federal Funds Purchased [Member]          
Short-term Debt [Line Items]          
Short-term borrowings 0   0   0
Short Term Borrowings, FHLB advances [Member]          
Short-term Debt [Line Items]          
Short-term borrowings 123,500   123,500   175,000
Maximum indebtedness $ 100,000 $ 465,000 $ 270,500 $ 465,000  
Maximum indebtedness, Rate 3.74% 4.44% 3.70% 4.44%  
End of period balance $ 123,500 $ 433,500 $ 123,500 $ 433,500  
End of period balance, Rate 4.13% 4.42% 4.13% 4.42%  
Average balance $ 107,823 $ 412,545 $ 128,127 $ 384,224  
Average rate paid 3.12% 4.42% 3.44% 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   $ 100,000
Interest rate on balance 3.78%   3.78%   3.81%
Short Term Borrowings, FHLB advances [Member] | Overnight [Member]          
Short-term Debt [Line Items]          
Short-term borrowings $ 23,500   $ 23,500   $ 75,000
Interest rate on balance 3.77%   3.77%   3.81%