Investments - Short-term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Adjusted Cost	$ 187,664	$ 72,859
Unrealized Gains	2	7
Unrealized Losses	(13)	(2)
Fair Value	187,653	72,864
Corporate bonds
Marketable Securities [Line Items]
Adjusted Cost	149,606	55,224
Unrealized Gains	1	5
Unrealized Losses	(12)	(2)
Fair Value	149,595	55,227
Government bonds
Marketable Securities [Line Items]
Adjusted Cost	15,499	14,121
Unrealized Gains	0	2
Unrealized Losses	0	0
Fair Value	15,499	14,123
Asset-backed bonds
Marketable Securities [Line Items]
Adjusted Cost	22,559	3,514
Unrealized Gains	1	0
Unrealized Losses	(1)	0
Fair Value	$ 22,559	$ 3,514