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Cash and Cash Equivalents and Investments in Marketable Securities (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Maximum term to maturity from date of purchase (years) 1 year  
Available-for-sale Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Investment Income, interest income on Marketable Securities $ 0.5hfc_InvestmentIncomeInterestIncomeOnMarketableSecurities
/ invest_InvestmentAxis
= us-gaap_AvailableforsaleSecuritiesMember		 $ 0.6hfc_InvestmentIncomeInterestIncomeOnMarketableSecurities
/ invest_InvestmentAxis
= us-gaap_AvailableforsaleSecuritiesMember