Investments (Tables)

9 Months Ended

Sep. 30, 2021

Investments Debt And Equity Securities [Abstract]

Schedule of Available-for-sale Investments

Available-for-sale investments consisted of the following as of September 30, 2021 and December 31, 2020 (in thousands):

	September 30, 2021
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities
U.S. government debt securities	$	277,331	$	87	$	—		$	277,418
Corporate bonds		15,225		1		(5	)		15,221
Total short-term marketable securities	$	292,556	$	88	$	(5	)	$	292,639
Long-term marketable securities
U.S. government debt securities	$	204,694	$	6	$	(74	)	$	204,626
Corporate bonds		12,761		—		(8	)		12,753
Total long-term marketable securities	$	217,455	$	6	$	(82	)	$	217,379

	December 31, 2020
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities
U.S. government debt securities	$	552,539	$	723	$	(10	)	$	553,252
Corporate bonds		11,497		86		(2	)		11,581
Total short-term marketable securities	$	564,036	$	809	$	(12	)	$	564,833
Long-term marketable securities
U.S. government debt securities	$	118,429	$	98	$	(2	)	$	118,525
Total long-term marketable securities	$	118,429	$	98	$	(2	)	$	118,525

Schedule of Gross Unrealized Holding Losses and Fair Value for Investments in Unrealized Loss Position

The following table presents the gross unrealized holding losses and fair value for investments in an unrealized loss position, and the length of time individual securities have been in a continuous loss position, as of September 30, 2021 (in thousands):

	Less Than 12 Months					12 Months Or Greater
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. government debt securities	$	163,664	$	(74	)	$	—	$	—
Corporate bonds		22,888		(13	)		—		—
Total available-for-sale securities	$	186,552	$	(87	)	$	—	$	—