Investments (Details 1) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investments:
Total	$ 19,351	$ 17,177
Financial assets measured at fair value on a recurring basis [Member] | Common Stock [Member]
Investments:
Available-for-sale securities - current:	954
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:	14,524
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:	3,873	2,821
Level 1 [Member]
Investments:
Total	4,827	2,821
Level 1 [Member] | Financial assets measured at fair value on a recurring basis [Member] | Common Stock [Member]
Investments:
Available-for-sale securities - current:	954
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:	3,873	2,821
Level 2 [Member]
Investments:
Total	14,524	14,356
Level 2 [Member] | Financial assets measured at fair value on a recurring basis [Member] | Common Stock [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]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents:		14,356
Investments:
Available-for-sale securities - current:	14,524
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] | Common Stock [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: