BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Detail) $ in Millions	Sep. 30, 2017 USD ($)
Significant Accounting Policies [Line Items]
Callable Debt Securities Held At Premium	$ 4.2
Callable Debt Securities Unamortized Premium	$ 0.1

Amount, after accumulated amortization, of debt premium on callable securities.

No definition available.

Name:	fbp_CallableDebtSecuritiesUnamortizedPremium
Namespace Prefix:	fbp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant