Litigation (Details)	9 Months Ended
Sep. 30, 2022 USD ($)
Litigation
Damages sought value	$ 5,000,000
Insured amount	3,000,000
Retention amount	1,000,000
Excess coverage policy	3,000,000
Payment as retention from excess coverage policy	$ 3,000,000
Former CEO
Litigation
Multiplier of severance Payment With Average Annual Compensation	2.99
Aero, Inc.
Litigation
Gain or loss on litigation	$ 0

Amount of excess (deficiency) of insurance coverage policy.

No definition available.

Name:	svt_AdditionalInsuranceCoveragePolicyAmount
Namespace Prefix:	svt_
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:	svt_LitigationLineItems
Namespace Prefix:	svt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The multiplier of severance payment with average annual compensation.

+ References

No definition available.

+ Details

Name:	svt_MultiplierOfSeverancePaymentWithAverageAnnualCompensation
Namespace Prefix:	svt_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of retention payable.

+ References

No definition available.

+ Details

Name:	svt_RetentionAmountPayable
Namespace Prefix:	svt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of payment from retention from the additional insurance coverage.

+ References

No definition available.

+ Details

Name:	svt_RetentionPayableAtAdditionalInsuranceCoverage
Namespace Prefix:	svt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

+ Details

Name:	us-gaap_GainLossRelatedToLitigationSettlement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of excess (deficiency) of insurance recovery over the loss incurred from an insured event.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 30
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

+ Details

Name:	us-gaap_InsuredEventGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349

+ Details

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

- Details

Name:	srt_TitleOfIndividualAxis=srt_ChiefExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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