Investments - Continuous Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses	$ (75)	$ (12)
Fair Value	84,811	128,502
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses	(63)	(6)
Fair Value	19,972	65,298
U.S. agency and government sponsored securities
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses	0	0
Fair Value	4,994	0
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses	(2)	(4)
Fair Value	35,934	47,629
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses	(9)	(2)
Fair Value	22,641	15,575
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses	(1)	0
Fair Value	$ 1,270	$ 0