3. CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS

Securities classified as cash, cash equivalents and short-term investments as of December 31, 2019 and December 31, 2018 are summarized below (in thousands). Estimated fair value is based on quoted market prices for these investments.


	December 31, 2019
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,124	$	—	$	—	$	3,124
Money market funds		147,208		—		—		147,208
Corporate bonds		11,441		—		—		11,441
Commercial paper		19,357		3		—		19,360
Total cash and cash equivalents	$	181,130	$	3	$	—	$	181,133
Short-term investments
Corporate bonds	$	21,690	$	6	$	(3)	$	21,693
Commercial paper		36,667		14		—		36,681
Asset-backed securities		8,005		—		—		8,005
Total short-term investments	$	66,362	$	20	$	(3)	$	66,379
Total cash equivalents and investments	$	247,492	$	23	$	(3)	$	247,512


	December 31, 2018
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,733	$	—	$	—	$	3,733
Money market funds		73,238		—		—		73,238
Commercial paper		1,797		—		—		1,797
Total cash and cash equivalents	$	78,768	$	—	$	—	$	78,768
Short-term investments
U.S. treasury securities	$	3,996	$	—	$	—	$	3,996
Corporate bonds		34,611		—		(21)		34,590
Commercial paper		41,371		—		(14)		41,357
Asset-backed securities		9,381		—		(3)		9,378
Total short-term investments	$	89,359	$	—	$	(38)	$	89,321
Total cash equivalents and investments	$	168,127	$	—	$	(38)	$	168,089

Cash equivalents consist of money market funds and other debt securities with original maturities of three months or less at the time of purchase, and the carrying amount is a reasonable approximation of fair value. The Company invests its cash in high quality securities of financial and commercial institutions. These securities are carried at fair value, which is based on readily available market information, with unrealized gains and losses included in accumulated other comprehensive income (loss) within stockholders’ equity on the Company’s balance sheets. The Company uses the specific identification method to determine the amount of realized gains or losses on sales of marketable securities. Realized gains or losses have been insignificant and are included in other income (expense), net, in the statement of operations.

All available-for-sale securities held as of December 31, 2019 and 2018, had contractual maturities of less than one year. The Company’s available-for-sale securities are subject to a periodic impairment review. The Company considers a debt 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 the statement of operations to its fair value and establishes that value 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 December 31, 2019 and 2018, no investment was in a continuous unrealized loss position for more than one year and the Company believes that it is more likely than not that the investments will be held until maturity or a forecasted recovery of fair value.