Financial Instruments - Summary of Cash and Cash Equivalents, Money Market Funds and Short-term Investments by Significant Investment Category (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	$ 273,734	$ 53,568
Unrealized Gains	11	1
Unrealized Losses	(29)	(2)
Market Value	273,716	53,567
Level 1 \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	20,292	16,366
Market Value	20,292	16,366
Level 2 \| U.S. Treasury Securities Included in Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	101,106	2,998
Unrealized Gains	5
Market Value	101,111	2,998
Level 2 \| U.S. Government Agency Securities Included in Cash and Cash equivalents and Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	66,998	34,204
Unrealized Gains	6	1
Unrealized Losses	(2)	(2)
Market Value	67,002	$ 34,203
Level 2 \| Corporate Debt Securities Included in Cash and Cash Equivalents and Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	85,338
Unrealized Gains	0
Unrealized Losses	(27)
Market Value	$ 85,311

Amortized cost of 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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