Investments

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Investments

5. Investments

Available-for-sale investments consisted of the following as of June 30, 2019 and December 31, 2018 (in thousands):

	June 30, 2019
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
	(unaudited)
Short-term marketable securities
Commercial paper	$	82,165	$	—	$	—		$	82,165
U.S. government debt and agency securities		269,366		351		(1	)		269,716
Corporate bonds		22,630		32		—			22,662
Total short-term marketable securities	$	374,161	$	383	$	(1	)	$	374,543

	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

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 June 30, 2019 (in thousands):

	Less Than 12 Months				12 Months Or Greater
	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
	(unaudited)
Short-term marketable securities
U.S. government debt and agency securities	$	—	$	—	$	4,997	$	(1	)
Total short-term marketable securities	$	—	$	—	$	4,997	$	(1	)

We evaluated our securities for other-than-temporary impairment and considered the decline in market value for the securities to be primarily attributable to current economic and market conditions. It is not more likely than not that we will be required to sell the securities, and we do not intend to do so prior to the recovery of the amortized cost basis. Based on this analysis, these marketable securities were not considered to be other-than-temporarily impaired as of June 30, 2019.

All the corporate debt, U.S. government and agency securities and commercial paper have an effective maturity date of less than one year.