Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FIDELITY SECURITIES FUND
Prospectus Date	rr_ProspectusDate	Sep. 29, 2016
07.31 Fidelity Series Small Cap Opportunities Fund F PRO-02 \| Fidelity® Series Small Cap Opportunities Fund
Risk/Return:	rr_RiskReturnAbstract
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Allocating the fund's assets across different market sectors (at present, consumer discretionary, consumer staples, energy, financials, health care, industrials, information technology, materials, real estate, telecom services, and utilities), using different Fidelity managers.

The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation 12B
-Number 240
-Section 12b
-Subsection 1

+ Details

Name:	dei_EntityRegistrantName
Namespace Prefix:	dei_
Data Type:	xbrli:normalizedStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The date of the prospectus.

+ References

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

+ Details

Name:	rr_ProspectusDate
Namespace Prefix:	rr_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	rr_RiskReturnAbstract
Namespace Prefix:	rr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Principal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 4
-Subsection a

+ Details

Name:	rr_StrategyNarrativeTextBlock
Namespace Prefix:	rr_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_DocumentInformationDocumentAxis=pbs_D0731FidelitySeriesSmallCapOpportunitiesFundFPRO02Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pbs_S000015587Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: