v3.25.3

Loans Receivable - Additional Information (Detail) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2025 USD ($) Loan	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) Loan
Schedule Of Activity Relating To Amount Due From Related Party [Line Items]
Number of loans \| Loan	9		9
Troubled debt restructuring	$ 16,700		$ 26,800
Residential Loan [Member]
Schedule Of Activity Relating To Amount Due From Related Party [Line Items]
Payments to Acquire Loans Receivable	74,200
Consumer Loans [Member]
Schedule Of Activity Relating To Amount Due From Related Party [Line Items]
Payments to Acquire Loans Receivable	5,100
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Schedule Of Activity Relating To Amount Due From Related Party [Line Items]
Financing receivable, accrued interest, writeoff	933	$ 692
Loans Receivable [Member]
Schedule Of Activity Relating To Amount Due From Related Party [Line Items]
Accrued Interest Receivable	$ 7,600		$ 6,500
Performing [Member]
Schedule Of Activity Relating To Amount Due From Related Party [Line Items]
Number of loans \| Loan	0		0

Number of loans modified financing receivable.

+ References

No definition available.

+ Details

Name:	bprn_NumberOfLoansModifiedFinancingReceivable
Namespace Prefix:	bprn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Schedule of activity relating to amount due from related party line item.

+ References

No definition available.

+ Details

Name:	bprn_ScheduleOfActivityRelatingToAmountDueFromRelatedPartyLineItems
Namespace Prefix:	bprn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of writeoff of accrued interest on financing receivable recognized by reversing interest income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3D
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3D

+ Details

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

- Definition

Accumulated amortized cost of financing receivable modified for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481746/310-40-50-4

+ Details

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

- Definition

The increase (decrease) during the reporting period in the amount due from borrowers for interest payments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

+ Details

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

- Definition

The cash outflow for the purchase of loan receivable arising from the financing of goods and services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-13

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Princeton Bancorp, Inc. 10-Q