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Fair Value of Financial Instruments (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Fair Value of Financial Instruments [Abstract]      
Investment maturity term 12 months 12 months  
Fair value of investments in rabbi trust $ 17,956   $ 17,843