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Significant Accounting Policies (Policy Liabilities) (Details)
 12 Months Ended
Dec. 31, 2014
Years of Issue, 1947 - 1968 [Member]  
Schedule of Liability for Life Insurance [Line Items]  
Traditional Life, Interest Rate 4.00%nsec_TraditionalLifeInterestRate
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsOfIssueRange1Member
Years of Issue, 1969 - 1978 [Member]  
Schedule of Liability for Life Insurance [Line Items]  
Traditional Life, Interest Rate, High End 6.00%us-gaap_TraditionalLifeInterestRateHighEnd
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsOfIssueRange2Member
Traditional Life, Interest Rate, Low End 5.00%us-gaap_TraditionalLifeInterestRateLowEnd
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsOfIssueRange2Member
Years of Issue, 1979 - 2003 [Member]  
Schedule of Liability for Life Insurance [Line Items]  
Traditional Life, Interest Rate, High End 7.00%us-gaap_TraditionalLifeInterestRateHighEnd
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsOfIssueRange3Member
Traditional Life, Interest Rate, Low End 6.00%us-gaap_TraditionalLifeInterestRateLowEnd
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsOfIssueRange3Member
Years of Issue, 2004 - 2012 [Member]  
Schedule of Liability for Life Insurance [Line Items]  
Traditional Life, Interest Rate 5.25%nsec_TraditionalLifeInterestRate
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsOfIssueRange4Member
Years of Issue, 2013 - 2014 [Member]  
Schedule of Liability for Life Insurance [Line Items]  
Traditional Life, Interest Rate 4.25%nsec_TraditionalLifeInterestRate
/ nsec_LifeInsuranceYearsOfIssueAxis
= nsec_LifeInsuranceYearsofIssueRange5Member