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Significant Accounting Policies (Concentration of Risk) (Details)
 12 Months Ended
Dec. 31, 2014
customer
Direct Written Premium [Member]  
Concentration Risk [Line Items]  
Concentration risk, other risk 0.05
Number of major customers 1nsec_NumberofMajorCustomers
/ us-gaap_ConcentrationRiskByTypeAxis
= nsec_DirectWrittenPremiumMember
P&C Insurance Operations [Member] | Geographic Concentration Risk [Member]  
Concentration Risk [Line Items]  
Number of states in which entity operates 8us-gaap_NumberOfStatesInWhichEntityOperates
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GeographicConcentrationRiskMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember
Life Insurance Operations [Member] | Geographic Concentration Risk [Member]  
Concentration Risk [Line Items]  
Number of states in which entity operates 7us-gaap_NumberOfStatesInWhichEntityOperates
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GeographicConcentrationRiskMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_LifeInsuranceSegmentMember
Sales Revenue, Segment [Member] | P&C Insurance Operations [Member] | Product Concentration Risk [Member]  
Concentration Risk [Line Items]  
Concentration risk, percentage 90.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember
Sales Revenue, Segment [Member] | P&C Insurance Operations [Member] | Geographic Concentration Risk [Member]  
Concentration Risk [Line Items]  
Concentration risk, percentage 60.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GeographicConcentrationRiskMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember
Sales Revenue, Segment [Member] | Life Insurance Operations [Member] | Product Concentration Risk [Member]  
Concentration Risk [Line Items]  
Concentration risk, percentage 10.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_LifeInsuranceSegmentMember
Sales Revenue, Segment [Member] | Life Insurance Operations [Member] | Geographic Concentration Risk [Member]  
Concentration Risk [Line Items]  
Concentration risk, percentage 79.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GeographicConcentrationRiskMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_LifeInsuranceSegmentMember