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Operating Segments - Narrative (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
partner_company
Dec. 31, 2013
Jun. 30, 2014
Mar. 31, 2014
Segment Reporting Information [Line Items]        
Non-consolidated partner companies 24sfe_PartnerCompaniesNotConsolidatedInFinancialStatements      
Other Segments [Member]        
Segment Reporting Information [Line Items]        
Total assets included cash, cash equivalents, cash held in escrow and marketable securities 156.5sfe_CashCashEquivalentsAndMarketableSecurities
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
$ 183.7sfe_CashCashEquivalentsAndMarketableSecurities
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
   
Bridgevine, Inc. [Member]        
Segment Reporting Information [Line Items]        
Ownership interest under equity method, percentage     17.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= sfe_BridgevineIncMember
22.70%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= sfe_BridgevineIncMember