FINANCIAL INSTRUMENTS WITH OFF-BALANCE-SHEET RISK (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Commitments to extend credit:
Commercial real estate loan committments	$ 33,580nvsl_LoanCommitments	$ 30,254nvsl_LoanCommitments
Unused home equity lines of credit	19,010	19,084
Commercial and industrial loan commitments	14,147	12,587
Amounts due on other commitments	9,170nvsl_AmountsDueOnOtherCommitments	7,257nvsl_AmountsDueOnOtherCommitments
Commercial letters of credit	$ 563nvsl_CommercialLettersOfCredit	$ 588nvsl_CommercialLettersOfCredit

It represents about the amount due on other commitments.

No definition available.

Name:	nvsl_AmountsDueOnOtherCommitments
Namespace Prefix:	nvsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

It represents the amount due on commercial and industrial loan commitments.

+ References

No definition available.

+ Details

Name:	nvsl_CommercialAndIndustrialLoanCommitments
Namespace Prefix:	nvsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

It represents the commercial letters of credit during the period.

+ References

No definition available.

+ Details

Name:	nvsl_CommercialLettersOfCredit
Namespace Prefix:	nvsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	nvsl_CommitmentsToExtendCreditAbstract
Namespace Prefix:	nvsl_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

It represents the loan commitments accounted for as derivatives, including the methods and assumptions used to estimate fair value and any associated hedging strategies.

+ References

No definition available.

+ Details

Name:	nvsl_LoanCommitments
Namespace Prefix:	nvsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of the fee for available but unused credit capacity under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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