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Fair Value of Financial Instruments (Narrative) (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Fair Value of Financial Instruments [Abstract]    
Investment maturity term 1 year  
Fair value of investments in rabbi trust $ 12,531,000 $ 10,872,000
Impairment charge, Held-to-maturity Securities $ 0