Investments (Tables)

12 Months Ended

Dec. 31, 2019

Investments Debt And Equity Securities [Abstract]

Schedule of Available-for-sale Investments

Available-for-sale investments consisted of the following as of December 31, 2019 and 2018 (in thousands):

	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 and agency 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 and agency 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

	December 31, 2018
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities
Commercial paper	$	16,887	$	—	$	—		$	16,887
U.S. government debt and agency securities		85,722		—		(99	)		85,623
Corporate bonds		7,486		—		(8	)		7,478
Total short-term marketable securities	$	110,095	$	—	$	(107	)	$	109,988

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

All the commercial paper, U.S. government debt and agency securities and corporate bonds designated as short-term marketable securities have an effective maturity date that is less than one year from the respective balance sheet date. Those that are designated as long-term marketable securities have an effective maturity date that is more than one year from the respective balance sheet date.

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, 2019 (in thousands):

	Less Than 12 Months					12 Months Or Greater
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. government debt and agency securities	$	30,196	$	(10	)	$	—	$	—
Corporate bonds		5,010		(3	)		—		—
Total available-for-sale securities	$	35,206	$	(13	)	$	—	$	—