v3.26.1

Mid Cap Value Portfolio Shareholder Fees	Dec. 31, 2025 USD ($)
Mid Cap Value Portfolio \| Mid Cap Value Portfolio
Prospectus [Line Items]
Shareholder Fee, Other

X

- References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-Section 1
-Subsection a

+ Details

Name:	oef_ProspectusLineItems
Namespace Prefix:	oef_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-Section 3
-Subsection instruction
-Paragraph 2

+ Details

Name:	oef_ShareholderFeeOther
Namespace Prefix:	oef_
Data Type:	dtr-types:nonNegativeMonetaryItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	dei_LegalEntityAxis=nmsf_S000000053Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	oef_ClassAxis=nmsf_C000000088Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: