3.Cash Equivalents and Investments

At September 30, 2018 and December 31, 2017, the balance in the Company’s accumulated other comprehensive income was comprised solely of activity related to the Company’s available‑for‑sale securities. There were no realized gains or losses recognized on the sale or maturity of available‑for‑sale securities during the three and nine months ended September 30, 2018 and 2017 and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive income for the same periods. All of the Company’s available-for-sale securities are subject to a periodic impairment review. The Company considers an investment security to be impaired when its fair value is less than its carrying cost, in which case the Company would further review the investment to determine whether it is other-than-temporarily impaired. When the Company evaluates an investment for other-than-temporary impairment, the Company reviews factors such as the length of time and extent to which fair value has been below cost basis, the financial condition of the issuer and any changes thereto, intent to sell, and whether it is more likely than not the Company will be required to sell the investment before the recovery of its cost basis. If an investment is other-than-temporarily impaired, the Company writes it down through earnings to its impaired value and establishes that as a new cost basis for the investment. The Company did not identify any of its available-for-sale securities as other-than-temporarily impaired in any of the periods presented. As of September 30, 2018, no investment was in a continuous unrealized loss position for more than one year, the unrealized losses were not due to change in credit risk, and the Company believes that it is more likely than not the investments will be held until maturity.

The following table summarizes the available‑for‑sale securities (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
September 30, 2018 (unaudited)
Money market funds	$	9,850	$	—	$	—		$	9,850
Corporate notes		31,749		—		(55	)		31,694
Commercial paper		83,744		—		—			83,744
Asset backed securities		12,226		—		(28	)		12,198
Government notes		12,448		—		(18	)		12,430
Total	$	150,017	$	—	$	(101	)	$	149,916

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2017:
Money market funds	$	8,685	$	—	$	—		$	8,685
Corporate notes		46,133		—		(35	)		46,098
Government notes		6,191		—		(16	)		6,175
Total	$	61,009	$	—	$	(51	)	$	60,958