Financial Instruments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Financial Instruments
Fair value assets, transfers from Level 1 to Level 2	$ 0		$ 0
Fair value assets, transfers from Level 2 to Level 1	0		0
Fair value liabilities, transfers from Level 1 to Level 2	0		0
Fair value liabilities, transfers from Level 2 to Level 1	$ 0		$ 0
Reverse repurchase agreements | Government Securities and Obligations | Minimum
Financial Instruments
Percentage of investment amount to collateralized deposits value	102.00%
Recurring
Summary of assets measured at fair value on a recurring basis
Total assets	$ 46,974	$ 33,714
Recurring | Level 1
Summary of assets measured at fair value on a recurring basis
Total assets	44,973	5,432
Recurring | Level 2
Summary of assets measured at fair value on a recurring basis
Total assets	2,001	28,282
Recurring | Money market fund
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents	44,973	5,432
Recurring | Money market fund | Level 1
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents	44,973	5,432
Recurring | Commercial Paper
Summary of assets measured at fair value on a recurring basis
Short-term investments		1,993
Recurring | Commercial Paper | Level 2
Summary of assets measured at fair value on a recurring basis
Short-term investments		1,993
Recurring | Corporate debt securities
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents		1,937
Short-term investments	2,001	3,352
Recurring | Corporate debt securities | Level 2
Summary of assets measured at fair value on a recurring basis
Cash and cash equivalents		1,937
Short-term investments	$ 2,001	3,352
Recurring | Reverse repurchase agreements
Summary of assets measured at fair value on a recurring basis
Short-term investments		21,000
Recurring | Reverse repurchase agreements | Level 2
Summary of assets measured at fair value on a recurring basis
Short-term investments		$ 21,000