Loans and Allowance for Credit Losses - Collateral Held Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance Allocated	$ 577	$ 499
Residential \| Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance Allocated	93	4
Residential \| Home equity lines of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance Allocated	69	40
Residential \| Closed end, first liens
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance Allocated	301	341
Residential \| Closed end, second liens
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance Allocated	114	114
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance Allocated		0
Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	60,237	58,741
Real Estate \| Residential \| Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	3,005	3,066
Real Estate \| Residential \| Home equity lines of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	10,736	9,748
Real Estate \| Residential \| Closed end, first liens
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	45,867	45,340
Real Estate \| Residential \| Closed end, second liens
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	629	469
Real Estate \| Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans		118
Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	0	0
Other \| Residential \| Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	0	0
Other \| Residential \| Home equity lines of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	0	0
Other \| Residential \| Closed end, first liens
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	0	0
Other \| Residential \| Closed end, second liens
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans	$ 0	0
Other \| Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually analyzed loans		$ 0

Amount of allowance for credit loss on financing receivable evaluated on individual basis. Excludes financing receivable evaluated on collective basis.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.5.a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480418/310-10-S99-4

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11B

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 30
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479391/326-20-30-2

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
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 of financing receivable individually evaluated for credit loss. Excludes financing receivable collectively evaluated for credit loss.

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=npb_ConstructionAndLandDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=npb_ClosedEndSecondLiensMember
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_CollateralAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CollateralAxis=npb_OtherCollateralTypeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: