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Investments - Schedule of Investments (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Investments schedule [Line Items]    
Investments, at fair value $ 6,641 $ 6,756
Rabbi Trust Associated With Deferred Compensation Plan [Member]    
Investments schedule [Line Items]    
Investments, at fair value 6,621 6,734
Equity Securities [Member]    
Investments schedule [Line Items]    
Investments, at fair value $ 20 $ 22