Investments (Tables)

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Schedule of Available-for-sale Investments

Available-for-sale investments consisted of the following as of December 31, 2020 and 2019 (in thousands):

	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

	December 31, 2019
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities
Commercial paper	$	121,866	$	—	$	—		$	121,866
U.S. government debt securities		285,963		394		(1	)		286,356
Corporate bonds		71,962		109		(3	)		72,068
Total short-term marketable securities	$	479,791	$	503	$	(4	)	$	480,290
Long-term marketable securities
U.S. government debt securities	$	90,750	$	146	$	(9	)	$	90,887
Corporate bonds		14,513		35		—			14,548
Total long-term marketable securities	$	105,263	$	181	$	(9	)	$	105,435

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 that individual securities have been in a continuous loss position as of December 31, 2020 (in thousands):

	Less Than 12 Months					12 Months Or Greater
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. government debt securities	$	177,554	$	(12	)	$	—	$	—
Corporate bonds		1,512		(2	)		—		—
Total available-for-sale securities	$	179,066	$	(14	)	$	—	$	—