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Fair Value of Financial Instruments (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Fair Value of Financial Instruments [Abstract]      
Investment maturity term 2 years    
Realized gains (losses) on available-for-sale securities $ 547 $ 0  
Fair value of investments in rabbi trust $ 17,179   $ 18,331