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Note J - Fair Value of Financial Instruments - Securities Measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Marketable equity securities $ 27,860 $ 26,664
Fair Value, Inputs, Level 1 [Member]    
Marketable equity securities 27,860  
Fair Value, Inputs, Level 2 [Member]    
Marketable equity securities 0  
Fair Value, Inputs, Level 3 [Member]    
Marketable equity securities $ 0