Financial Instruments (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Summary of assets measured at fair value on a recurring basis
Total assets	$ 33,714	$ 33,180
Level 1
Summary of assets measured at fair value on a recurring basis
Total assets	5,432	5,956
Level 2
Summary of assets measured at fair value on a recurring basis
Total assets	28,282	27,224
Money market fund
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents	5,432	5,956
Money market fund | Level 1
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents	5,432	5,956
Commercial Paper
Summary of assets measured at fair value on a recurring basis
Short-term investments	1,993
Commercial Paper | Level 2
Summary of assets measured at fair value on a recurring basis
Short-term investments	1,993
Corporate debt securities
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents	1,937	1,948
Short-term investments	3,352	7,276
Corporate debt securities | Level 2
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents	1,937	1,948
Short-term investments	3,352	7,276
Reverse repurchase agreements
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents		3,000
Short-term investments	21,000	15,000
Reverse repurchase agreements | Level 2
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents		3,000
Short-term investments	$ 21,000	$ 15,000