Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Assets
Financial assets, fair value	$ 68,216	$ 71,458
U.S. government securities
Financial Assets
Financial assets, fair value		4,112
Money market funds
Financial Assets
Financial assets, fair value	7,023	7,180
Reverse repurchase agreements
Financial Assets
Financial assets, fair value	6,250	6,250
Commercial paper
Financial Assets
Financial assets, fair value	15,193	53,916
Corporate bonds
Financial Assets
Financial assets, fair value	39,750
Level 1
Financial Assets
Financial assets, fair value	7,023	7,180
Level 1 | Money market funds
Financial Assets
Financial assets, fair value	7,023	7,180
Level 2
Financial Assets
Financial assets, fair value	61,193	64,278
Level 2 | U.S. government securities
Financial Assets
Financial assets, fair value		4,112
Level 2 | Reverse repurchase agreements
Financial Assets
Financial assets, fair value	6,250	6,250
Level 2 | Commercial paper
Financial Assets
Financial assets, fair value	15,193	$ 53,916
Level 2 | Corporate bonds
Financial Assets
Financial assets, fair value	$ 39,750