Quarterly report pursuant to Section 13 or 15(d)

Investments (Details 2)

v2.4.1.9
Investments (Details 2) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Trading securities portfolio      
Trading securities portfolio $ 1,118us-gaap_TradingSecuritiesRestricted   $ 1,038us-gaap_TradingSecuritiesRestricted
Gains 23us-gaap_TradingSecuritiesRealizedGain 15us-gaap_TradingSecuritiesRealizedGain  
U.S. government security funds      
Trading securities portfolio      
Net Unrealized Losses $ 8natr_AvailableForSaleSecuritiesNetUnrealizedLosses
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember
  $ 15natr_AvailableForSaleSecuritiesNetUnrealizedLosses
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentDebtSecuritiesMember