Cash and Marketable Securities - Components of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	May 31, 2021	Dec. 31, 2020
Short-term marketable securities
Amortized Cost	$ 10,199		$ 90,034
Unrealized Holding Gains (Losses)	(2)		(136)
Fair Value	10,197		89,898
Long-term marketable securities
Amortized Cost	5,500
Unrealized Holding Gains (Losses)	(167)
Fair Value	5,333
Amortized Cost	15,699
Unrealized Holding Gains (Losses)	(169)
Fair Value	15,530
Corporate debt securities
Short-term marketable securities
Amortized Cost	10,199		90,034
Unrealized Holding Gains (Losses)	(2)		(136)
Fair Value	10,197		$ 89,898
Long-term marketable securities
Debt securities, amortized cost	500
Debt securities, unrealized holding gains (losses)	0
Fair value	500
Corporate equity securities
Long-term marketable securities
Equity securities, amortized cost	5,000	$ 5,000
Equity securities, unrealized holding gains (losses)	(167)
Corporate equity securities	$ 4,833