Summary of Significant Accounting Policies - Purchased Credit Deteriorated Loans (Details)	12 Months Ended
Dec. 31, 2021 USD ($)
Accounting Policies [Abstract]
Credit loss expense recognized upon acquisition of a PCD loan	$ 0

Financing Receivable, Excluding Accrued Interest, Allowance For Credit Loss, Purchased With Credit Deterioration, Increase

No definition available.

Name:	fbnc_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossPurchasedWithCreditDeteriorationIncrease
Namespace Prefix:	fbnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration