Quarterly report pursuant to Section 13 or 15(d)

Cash Equivalents and Investments (Schedule of Estimated Fair Value of Available-for-Sale Securities) (Details)

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Cash Equivalents and Investments (Schedule of Estimated Fair Value of Available-for-Sale Securities) (Details) - Investments [Member]
$ in Thousands
Mar. 31, 2018
USD ($)
Schedule of Available-for-sale Securities [Line Items]  
Amortized Cost, Due within one year $ 6,026
Estimated Market Value, Due within one year $ 6,019