Impact of new accounting Principle in allowance for credit losses of held to maturity secutities.

No definition available.

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

- Definition

Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118955202&loc=SL82895884-210446

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

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

- Definition

Amount of allowance for credit loss at acquisition date of investment in debt security measured at amortized cost (held-to-maturity), purchased with credit deterioration.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 19
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919265-210447

+ Details

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

- 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

No definition available.

+ Details

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

- Definition

Amount of expense related to credit loss from transactions other than loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

+ Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_PR
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	fbp_CumulativeEffectPeriodOfAdoptionAxis=fbp_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InformationByCategoryOfDebtSecurityAxis=us-gaap_HeldtomaturitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

INVESTMENT SECURITIES - ACL on Debt Securities Held-To-Maturity (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Sep. 01, 2020	Sep. 30, 2020	Sep. 30, 2020	Jul. 01, 2020	Jan. 01, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning Balance			$ 0
Initial allowance on PCD debt securities	$ 1,269
Ending Balance		$ 10,176	10,176
Municipal Bonds [Member] \| PUERTO RICO
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning Balance		9,268	0
Initial allowance on PCD debt securities	$ 1,269
Ending Balance		10,176	10,176
Municipal Bonds [Member] \| PUERTO RICO \| ASC 326
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Ending Balance		10,200	10,200
Municipal Bonds [Member] \| PUERTO RICO \| ASC 326 \| Cumulative Effect Period Of Adoption Adjustment [Member]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Impact of adopting ASC 326 on Held-to-maturity securities				$ 0	$ 8,134
Municipal Bonds [Member] \| PUERTO RICO \| Held-to-maturity Securities [Member]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Provision for credit loss expense		$ (361)	$ 773