Fair Value Measurements (Details) - Recurring - Money market funds, US Government Securities and Agency Investments - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Total
Fair Value Measurements
Money market funds, U.S. Government Securities and Agency Investments	$ 172,119	$ 116,872
Level 1
Fair Value Measurements
Money market funds, U.S. Government Securities and Agency Investments	$ 172,119	92,872
Level 2
Fair Value Measurements
Money market funds, U.S. Government Securities and Agency Investments		$ 24,000