Short-Term and Other Borrowings - Summary of Federal Funds Purchased, Securities Sold Under Agreements to Repurchase and Other Short-term Borrowings (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Short-term Debt [Line Items]
Long-Term Subordinated Debentures	$ 73,718,000		$ 73,718,000		$ 73,594,000
Total Subordinated Debentures	104,067,000		104,067,000		103,943,000
First Citizens Statutory Trust II [Member]
Short-term Debt [Line Items]
Subordinated Debentures	7,732,000		7,732,000		7,732,000
First Citizens Statutory Trust III [Member]
Short-term Debt [Line Items]
Subordinated Debentures	12,887,000		12,887,000		12,887,000
First Citizens Statutory Trust IV [Member]
Short-term Debt [Line Items]
Subordinated Debentures	5,082,000		5,082,000		5,082,000
Futura TPF Trust I [Member]
Short-term Debt [Line Items]
Subordinated Debentures	2,578,000		2,578,000		2,578,000
Futura TPF Trust II [Member]
Short-term Debt [Line Items]
Subordinated Debentures	2,070,000		2,070,000		2,070,000
Short Term Borrowings, FHLB advances [Member]
Short-term Debt [Line Items]
Short-term borrowings	287,047,000		287,047,000		338,041,000
Maximum indebtedness	497,500,000	$ 431,500,000	501,500,000	$ 540,000,000
Average balance	$ 388,022,000	$ 233,547,000	$ 385,801,000	$ 282,214,000
Average rate paid	5.35%	5.51%	5.42%	5.03%
Short Term Borrowings, FHLB advances [Member] | Single Maturity Fixed Rate [Member]
Short-term Debt [Line Items]
Short-term borrowings	$ 47,000		$ 47,000		$ 41,000
Interest rate on balance	1.18%		1.18%		1.25%
Short Term Borrowings, FHLB advances [Member] | Overnight [Member]
Short-term Debt [Line Items]
Short-term borrowings	$ 287,000,000		$ 287,000,000		$ 338,000,000
Interest rate on balance	4.88%		4.88%		5.41%