ALLOWANCE FOR CREDIT LOSSES FOR LOANS AND FINANCE LEASES - Activity in ACL on Loans and Finance Leases (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	$ 247,269	$ 263,592	$ 243,942	$ 261,843
Provision for credit losses - expense (benefit)	20,381	11,930	45,218	24,847
Charge-offs	(24,529)	(26,414)	(52,739)	(55,753)
Recoveries	5,457	5,424	12,157	23,595
Ending balance	248,578	254,532	248,578	254,532
Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance			0
Residential Portfolio Segment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	41,640	56,689	40,654	57,397
Provision for credit losses - expense (benefit)	793	(10,593)	1,797	(11,057)
Charge-offs	(285)	(491)	(520)	(1,007)
Recoveries	300	446	517	718
Ending balance	42,448	46,051	42,448	46,051
Residential Portfolio Segment [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance			0
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	3,417	6,186	3,824	5,605
Provision for credit losses - expense (benefit)	1,121	(554)	700	17
Charge-offs	0	0	0	0
Recoveries	13	14	27	24
Ending balance	4,551	5,646	4,551	5,646
Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance			0
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	24,143	32,661	22,447	32,631
Provision for credit losses - expense (benefit)	(1,448)	(2,976)	208	(2,986)
Charge-offs	0	0	0	0
Recoveries	51	393	91	433
Ending balance	22,746	30,078	22,746	30,078
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance			0
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	36,464	35,423	33,034	33,996
Provision for credit losses - expense (benefit)	2,135	(596)	5,488	(3,756)
Charge-offs	(66)	(348)	(143)	(880)
Recoveries	826	961	980	6,080
Ending balance	39,359	35,440	39,359	35,440
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance			0
Consumer Portfolio Segment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	141,605	132,633	143,983	132,214
Provision for credit losses - expense (benefit)	17,780	26,649	37,025	42,629
Charge-offs	(24,178)	(25,575)	(52,076)	(53,866)
Recoveries	4,267	3,610	10,542	16,340
Ending balance	139,474	137,317	139,474	137,317
Consumer Portfolio Segment [Member] \| Bulk Sale Of Fully Charged-Off Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Recoveries	$ 2,400	$ 9,500	2,400	$ 9,500
Consumer Portfolio Segment [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance			$ 0

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Definition

Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Details

Name:	srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
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_CommercialPortfolioSegmentMember
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:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialAndIndustrialSectorMember
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_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis=fbp_BulkSaleOfFullyChargedOffLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: