3. Cash Equivalents, Marketable Securities and Equity Securities

Cash equivalents, marketable securities and equity securities consisted of the following at September 30, 2018 (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
September 30, 2018	Cost		Gains		Losses		Value
Cash equivalents and marketable securities:
Money market funds	$	106,974	$	—	$	—	$	106,974
U.S. Treasuries		200,437		—		(67)		200,370
Government agency securities		29,922		—		(15)		29,907
Equity securities included in other non-current assets:
Corporate equity securities		3,667		—		—		3,667
Total	$	341,000	$	—	$	(82)	$	340,918

Cash equivalents and marketable securities consisted of the following at December 31, 2017 (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
December 31, 2017	Cost		Gains		Losses		Value
Cash equivalents and marketable securities:
Money market funds	$	134,635	$	—	$	—	$	134,635
U.S. Treasuries		135,601		—		(47)		135,554
Government agency securities		58,979		—		(29)		58,950
Total	$	329,215	$	—	$	(76)	$	329,139

At September 30, 2018, the Company held 41 securities that were in an unrealized loss position. The aggregate fair value of securities held by the Company in an unrealized loss position for less than 12 months at September 30, 2018 was $230.3 million, and there were no securities held by the Company in an unrealized loss position for more than 12 months. Pursuant to the adoption of ASU 2016-01, the Company records changes in the fair value of its investments in corporate equity securities to “Other income (expense), net” in the Company’s condensed consolidated statements of operations. The Company records unrealized gains (losses) on available-for-sale debt securities as a component of accumulated other comprehensive income (loss) until such gains and losses are realized.

As of September 30, 2018, the Company did not intend to sell, and would not be more likely than not required to sell, the debt securities in an unrealized loss position before recovery of their amortized cost bases. Furthermore, the Company has determined that there were no material changes in the credit risk of the debt securities. As a result, the Company determined it did not hold any marketable securities with any other-than-temporary impairment as of September 30, 2018.

There were no realized gains or losses on available-for-sale securities during the nine months ended September 30, 2018 or 2017.