The Company’s investment strategy is focused on capital preservation. The Company invests in instruments that meet the credit quality standards outlined in the Company’s investment policy. This policy also limits the amount of credit exposure to any one issue or type of instrument. As of June 30, 2019, and December 31, 2018, the Company’s investments were in government money market funds, certificates of deposit, commercial paper and corporate debt securities. There were no sales of available-for-sale securities during the three and six months ended June 30, 2019 or during the year ended December 31, 2018.

Investments classified as available-for-sale as of June 30, 2019 consisted of the following (in thousands):

As of June 30, 2019	Amortized Cost		Gross Unrealized Gains ⁽¹⁾		Gross Unrealized Losses ⁽¹⁾			Aggregate Estimated Fair Value
Certificate of deposit ⁽²⁾	$	251	$	—	$	—		$	251
Corporate debt securities ⁽²⁾		273,022		261		(21	)		273,262
	$	273,273	$	261	$	(21	)	$	273,513

(1)

Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At June 30, 2019, there were 136 securities in an unrealized gain position and there were 36 securities in an unrealized loss position. The unrealized gains were less than $20,000 individually and $261,000 in the aggregate. The unrealized losses were less than $4,000 individually and $21,000 in the aggregate. These securities have not been in a continuous unrealized gain or loss position for more than 12 months. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value.

Investments classified as available-for-sale as of December 31, 2018 consisted of the following (in thousands):

As of December 31, 2018	Amortized Cost		Gross Unrealized Gains ⁽¹⁾		Gross Unrealized Losses ⁽¹⁾			Aggregate Estimated Fair Value
Commercial paper ⁽²⁾	$	3,479	$	—	$	—		$	3,479
Corporate debt securities ⁽²⁾		273,677		1		(416	)		273,262
	$	277,156	$	1	$	(416	)	$	276,741

(1)

Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At December 31, 2018, there were 181 securities in an unrealized loss position and three securities in an unrealized gain position. The unrealized losses were less than $17,000 individually and $416,000 in the aggregate. The unrealized gains were less than $1,000 individually and $1,000 in the aggregate. These securities have not been in a continuous unrealized loss position for more than 12 months. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value.