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Long-Term Debt - Summary of long term debt (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Long-term debt $ 4,620us-gaap_LongTermDebt $ 2,662us-gaap_LongTermDebt
Less current portion (548)us-gaap_LongTermDebtCurrent (2,641)us-gaap_LongTermDebtCurrent
Long-term debt, Noncurrent 4,072us-gaap_LongTermDebtNoncurrent 21us-gaap_LongTermDebtNoncurrent
Term loan payable to a financial institution    
Debt Instrument [Line Items]    
Long-term debt 2,620us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember		   
Term loan payable to a financial institution    
Debt Instrument [Line Items]    
Long-term debt 2,000us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= svt_TermLoanPayableToFinancialInstitutionMember		   
Industrial Development Revenue Bonds    
Debt Instrument [Line Items]    
Long-term debt    2,620us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= svt_IndustrialDevelopmentRevenueBondsMember
Secured term loan payable to government agency    
Debt Instrument [Line Items]    
Long-term debt    $ 42us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= svt_SecuredTermLoanPayableToGovernmentAgencyMember