For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-21

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-20

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-20

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ 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

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CreditConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_LoansReceivableMember
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_FinancingReceivablePortfolioSegmentAxis=fbp_OverallTotalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

ALLOWANCE FOR CREDIT LOSSES FOR LOANS AND FINANCE LEASES - Carrying Amount of Portfolios (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024	Jun. 30, 2025	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 13,048,684	$ 12,746,556
Allowance for credit losses	246,990	243,942	$ 248,578	$ 246,996	$ 254,532	$ 261,843
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	2,889,081	2,828,431
Allowance for credit losses	$ 40,272	$ 40,654	42,448	40,651	46,051	57,397
Residential Mortgage Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.39%	1.44%
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 259,863	$ 228,396
Allowance for credit losses	$ 5,360	$ 3,824	4,551	3,998	5,646	5,605
Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	2.06%	1.67%
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 2,549,375	$ 2,565,984
Allowance for credit losses	$ 25,366	$ 22,447	22,746	24,205	30,078	32,631
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	0.99%	0.87%
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 3,614,241	$ 3,366,038
Allowance for credit losses	$ 37,854	$ 33,034	39,359	35,099	35,440	33,996
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.05%	0.98%
Consumer Portfolio Segment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 3,736,124	$ 3,757,707
Allowance for credit losses	$ 138,138	$ 143,983	$ 139,474	$ 143,043	$ 137,317	$ 132,214
Consumer Portfolio Segment [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	3.70%	3.83%
Loan Total [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.89%	1.91%