Investments - Short-term Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Adjusted Cost	$ 235,156	$ 72,859
Unrealized Gains	3	7
Unrealized Losses	(62)	(2)
Fair Value	235,097	72,864
Corporate bonds
Marketable Securities [Line Items]
Adjusted Cost	177,273	55,224
Unrealized Gains	1	5
Unrealized Losses	(53)	(2)
Fair Value	177,221	55,227
Government bonds
Marketable Securities [Line Items]
Adjusted Cost	40,955	14,121
Unrealized Gains	2	2
Unrealized Losses	(5)	0
Fair Value	40,952	14,123
Asset-backed bonds
Marketable Securities [Line Items]
Adjusted Cost	16,928	3,514
Unrealized Gains	0	0
Unrealized Losses	(4)	0
Fair Value	$ 16,924	$ 3,514

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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