Loans Receivable and the Allowance for Credit Losses - Narrative (Details)	12 Months Ended
Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Loans Receivable and the Allowance for Loan Losses
Loans serviced for the benefit of others	$ 40,729,000,000	$ 22,350,000,000
Sale of loan participations	$ 19,200,000	$ 11,500,000
Number of loans sold \| loan	3	1
Sale of loan par totaling	$ 10,400,000	$ 1,578,000,000
Sale of loan interest reserve		63,000,000
Gain (loss) on sale of loans	159,000	391,000,000
Individually evaluated loans	$ 4,400,000	855,000
Financing receivable individually evaluated for impairment, nonaccrual number \| loan	2
Interest income recognized from individually evaluated loans	$ 0	$ 0
Non-accrual loans \| loan		0
Number of loans modified that were deemed troubled debt restructuring \| loan	0	0
Construction
Loans Receivable and the Allowance for Loan Losses
Number of loans individually evaluated for impairment \| loan	2

Amount of interest income on financing receivable that were individually evaluated for impairment.

No definition available.

Name:	necb_FinancingReceivableIndividuallyEvaluatedForImpairmentInterestIncome
Namespace Prefix:	necb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of financing receivable individually evaluated for impairment on non accrual status.

+ References

No definition available.

+ Details

Name:	necb_FinancingReceivableIndividuallyEvaluatedForImpairmentNonaccrualNumber
Namespace Prefix:	necb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of financing receivables that were individually evaluated for impairment.

+ References

No definition available.

+ Details

Name:	necb_FinancingReceivableIndividuallyEvaluatedForImpairmentNumberOfLoans
Namespace Prefix:	necb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying amount of loans receivable serviced for the benefit of others.

+ References

No definition available.

+ Details

Name:	necb_LoansServicedForBenefitOfOthers
Namespace Prefix:	necb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of Nonaccrual Loans.

+ References

No definition available.

+ Details

Name:	necb_NonaccrualLoans
Namespace Prefix:	necb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of loans modified that were deemed troubled debt restructuring.

+ References

No definition available.

+ Details

Name:	necb_NumberOfLoansModifiedThatWereDeemedTroubledDebtRestructuring
Namespace Prefix:	necb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents information pertaining to number of loans sold.

+ References

No definition available.

+ Details

Name:	necb_NumberOfLoansSold
Namespace Prefix:	necb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from sale of loan participations.

+ References

No definition available.

+ Details

Name:	necb_ProceedsFromSaleOfLoanParticipations
Namespace Prefix:	necb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents information pertaining to sale of loan interest reserve.

+ References

No definition available.

+ Details

Name:	necb_SaleOfLoanInterestReserve
Namespace Prefix:	necb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11C

Reference 2: 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

+ Details

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

- Definition

The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans and leases that were sold during the reporting period. This element refers to the gain (loss) and not to the cash proceeds of the sales. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

+ Details

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

- Definition

The cash inflow resulting from the sale of loans classified as held-for-sale, including proceeds from loans sold through mortgage securitization.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-16

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-21

+ Details

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

- Details

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