Long-Term Debt (Detail Textuals) (USD $) In Thousands, unless otherwise specified			9 Months Ended
Sep. 30, 2013 Line of credit	Dec. 31, 2012 Line of credit	Sep. 30, 2013 Industrial Development Revenue Bonds; secured by an equivalent letter of credit from a bank with interest payable monthly at a floating rate (0.32% at September 30, 2013) Letter of credit from bank
Debt Instrument [Line Items]
Annual sinking fund payments commenced December 1, 2000 through 2013			$ 170
Percentage of annual fee of secured amount			1.00%
Percentage of annual fee of principal amount outstanding			0.25%
Final sinking fund payment due December 1, 2014			2,620
Unsecured line of credit	$ 2,000	$ 2,000

Amount to be paid into a fund, which is used to retire the debt instrument.

No definition available.

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Namespace Prefix:	svt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of annual fee of principal amount outstanding.

+ References

No definition available.

+ Details

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Namespace Prefix:	svt_
Data Type:	num:percentItemType
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Period Type:	instant

- Definition

Percentage of annual fee of secured amount.

+ References

No definition available.

+ Details

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Namespace Prefix:	svt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Amount paid into a fund, which is used to retire the debt instrument.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the 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

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Balance Type:	credit
Period Type:	instant