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Shareholders' Equity (Detail Textuals) (Share Repurchase Program)
3 Months Ended
Mar. 31, 2015
Share Repurchase Program
 
Equity, Class of Treasury Stock [Line Items]  
Number of common shares authorized to be purchased (in shares) 450,000us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased
/ us-gaap_ShareRepurchaseProgramAxis
= svt_ShareRepurchaseProgramMember
Remaining number of shares authorized to be purchased (in shares) 331,970us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased
/ us-gaap_ShareRepurchaseProgramAxis
= svt_ShareRepurchaseProgramMember
Shares purchased during period (in shares) 118,030us-gaap_StockRepurchasedDuringPeriodShares
/ us-gaap_ShareRepurchaseProgramAxis
= svt_ShareRepurchaseProgramMember