LOAN PORTFOLIO - Loan Modifications are Considered TDRs (Detail) - Entity Loan Modification Program [Member] $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) numberofcontracts	Dec. 31, 2017 USD ($) numberofcontracts	Dec. 31, 2016 USD ($) numberofcontracts
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	1,228	1,275	2,228
Pre-modification Outstanding Recorded Investment	$ 173,082	$ 94,796	$ 86,106
Post-Modification Outstanding Recorded Investment	$ 171,857	$ 93,837	$ 84,942
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	10	21	25
Pre-modification Outstanding Recorded Investment	$ 9,141	$ 39,428	$ 22,182
Post-Modification Outstanding Recorded Investment	$ 8,786	$ 39,338	$ 22,184
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	11	13	11
Pre-modification Outstanding Recorded Investment	$ 138,994	$ 25,722	$ 5,710
Post-Modification Outstanding Recorded Investment	$ 138,785	$ 25,018	$ 5,739
Finance Leases Portfolio Segment [Member] \| Consumer Loan [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	48	22	74
Pre-modification Outstanding Recorded Investment	$ 1,001	$ 548	$ 1,878
Post-Modification Outstanding Recorded Investment	$ 987	$ 548	$ 1,878
Other Loans [Member] \| Residential Portfolio Segment [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	104	132	209
Pre-modification Outstanding Recorded Investment	$ 14,827	$ 19,484	$ 30,940
Post-Modification Outstanding Recorded Investment	$ 14,159	$ 19,263	$ 29,668
Other Loans [Member] \| Consumer Portfolio Segment [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	768	657	1,156
Pre-modification Outstanding Recorded Investment	$ 3,935	$ 3,041	$ 5,496
Post-Modification Outstanding Recorded Investment	$ 3,996	$ 3,094	$ 5,576
Construction loans [Member] \| Residential Portfolio Segment [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	1
Pre-modification Outstanding Recorded Investment	$ 587
Post-Modification Outstanding Recorded Investment	$ 558
Construction loans [Member] \| Commercial Portfolio Segment [Member] \| Land [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	1	4	9
Pre-modification Outstanding Recorded Investment	$ 97	$ 122	$ 6,759
Post-Modification Outstanding Recorded Investment	$ 97	$ 125	$ 6,756
Auto loans [Member] \| Consumer Portfolio Segment [Member]
Financing Receivable Modifications [Line Items]
Number of contracts \| numberofcontracts	285	426	744
Pre-modification Outstanding Recorded Investment	$ 4,500	$ 6,451	$ 13,141
Post-Modification Outstanding Recorded Investment	$ 4,489	$ 6,451	$ 13,141

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationNameAxis=us-gaap_EntityLoanModificationProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquitySecuritiesByIndustryAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_MortgageReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbp_OtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_LandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_AutomobileLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: