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Investments (Narrative) (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Investments [Abstract]      
Losses from oher-than-temporary impairment charges $ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetAvailableforsaleSecurities $ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetAvailableforsaleSecurities  
Carrying value, Noncurrent 4,570,000us-gaap_AvailableForSaleSecuritiesNoncurrent 59,768,000us-gaap_AvailableForSaleSecuritiesNoncurrent  
Proceeds from sales of investments available-for-sale 441,430,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities 696,534,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities 1,350,003,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Gross realized gains 5,700,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains 26,400,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains 37,200,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Gross realized losses $ 3,000,000us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses $ 2,400,000us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses $ 500,000us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses