Investments (Details 1) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investments:
Total	$ 19,217	$ 17,177
Financial assets measured at fair value on a recurring basis [Member] | Marketable securities [Member]
Investments:
Available-for-sale securities - current:	790
Financial assets measured at fair value on a recurring basis [Member] | U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:		14,356
Investments:
Available-for-sale securities - current:	14,668
Money market funds [Member] | Financial assets measured at fair value on a recurring basis [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:	3,759	2,821
Level 1 [Member]
Investments:
Total	4,549	2,821
Level 1 [Member] | Financial assets measured at fair value on a recurring basis [Member] | Marketable securities [Member]
Investments:
Available-for-sale securities - current:	790
Level 1 [Member] | Financial assets measured at fair value on a recurring basis [Member] | U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:
Investments:
Available-for-sale securities - current:
Level 1 [Member] | Money market funds [Member] | Financial assets measured at fair value on a recurring basis [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:	3,759	2,821
Level 2 [Member]
Investments:
Available-for-sale securities - current:		14,356
Total	14,668	14,356
Level 2 [Member] | Financial assets measured at fair value on a recurring basis [Member] | Marketable securities [Member]
Investments:
Available-for-sale securities - current:
Level 2 [Member] | Financial assets measured at fair value on a recurring basis [Member] | U.S. Treasury securities [Member]
Investments:
Available-for-sale securities - current:	14,668
Level 2 [Member] | Money market funds [Member] | Financial assets measured at fair value on a recurring basis [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:
Level 3 [Member]
Investments:
Total
Level 3 [Member] | Financial assets measured at fair value on a recurring basis [Member] | Marketable securities [Member]
Investments:
Available-for-sale securities - current:
Level 3 [Member] | Financial assets measured at fair value on a recurring basis [Member] | U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:
Investments:
Available-for-sale securities - current:
Level 3 [Member] | Money market funds [Member] | Financial assets measured at fair value on a recurring basis [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents: