Investments (Details 1) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investments:
Total	$ 18,159	$ 19,217
Financial assets measured at fair value on a recurring basis [Member] | Marketable securities [Member]
Investments:
Available-for-sale securities - current:	120	790
Financial assets measured at fair value on a recurring basis [Member] | U.S. Treasury securities [Member]
Investments:
Available-for-sale securities - current:	9,945	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:	8,094	3,759
Level 1 [Member]
Investments:
Total	8,214	4,549
Level 1 [Member] | Financial assets measured at fair value on a recurring basis [Member] | Marketable securities [Member]
Investments:
Available-for-sale securities - current:	120	790
Level 1 [Member] | Financial assets measured at fair value on a recurring basis [Member] | U.S. Treasury securities [Member]
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:	8,094	3,759
Level 2 [Member]
Investments:
Total	9,945	14,668
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:	9,945	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]
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: