Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details)

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Fair Value Measurements (Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents $ 5,722 $ 6,193
Assets (Liabilities) Net, fair value 11,828 11,734
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 5,722 6,193
Assets (Liabilities) Net, fair value 5,722 6,193
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets (Liabilities) Net, fair value 6,106 5,541
Money Market Funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 5,722 6,193
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 5,722 6,193
Short-Term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 6,106 5,541
Short-Term Investments [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 6,106 5,541
Short-Term Investments [Member] | Corporate Notes/Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 1,510 4,544
Short-Term Investments [Member] | Corporate Notes/Bonds [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 1,510 4,544
Short-Term Investments [Member] | Commercial Paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 4,596 997
Short-Term Investments [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 4,596 $ 997