Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS (Details)

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FAIR VALUE MEASUREMENTS (Details) - Cash and Cash Equivalents - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]    
Adjusted Cost $ 77,515 $ 73,633
Gross Unrealized Losses (18) (25)
Fair Value 77,497 73,608
Municipal bonds and notes    
Debt Securities, Available-for-sale [Line Items]    
Adjusted Cost 553 13,320
Gross Unrealized Losses 0 (1)
Fair Value 553 13,319
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Adjusted Cost 35,857 49,432
Gross Unrealized Losses (18) (24)
Fair Value 35,839 49,408
Financial institution instruments    
Debt Securities, Available-for-sale [Line Items]    
Adjusted Cost 41,105 10,881
Gross Unrealized Losses 0 0
Fair Value $ 41,105 $ 10,881