Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair value measurements
Estimated Fair Value	$ 130,766	$ 281,783
Recurring fair value measurement
Fair value measurements
Estimated Fair Value	130,766	281,743
Recurring fair value measurement | Money market funds
Fair value measurements
Estimated Fair Value	130,766	281,743
Recurring fair value measurement | Level 1
Fair value measurements
Estimated Fair Value	130,766	281,743
Recurring fair value measurement | Level 1 | Money market funds
Fair value measurements
Estimated Fair Value	130,766	281,743
Recurring fair value measurement | Level 2
Fair value measurements
Estimated Fair Value	0	0
Recurring fair value measurement | Level 2 | Money market funds
Fair value measurements
Estimated Fair Value	0	0
Recurring fair value measurement | Level 3
Fair value measurements
Estimated Fair Value	0	0
Recurring fair value measurement | Level 3 | Money market funds
Fair value measurements
Estimated Fair Value	$ 0	$ 0