Securities classified as cash, cash equivalents and short-term investments as of September 30, 2018 and December 31, 2017, are summarized below (in thousands). Estimated fair value is based on quoted market prices for these investments.


	September 30, 2018
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	2,787		—		—	$	2,787
Money market funds		66,235		—		—		66,235
Corporate bonds		1,999		—		—		1,999
Commercial paper		3,994		—		—		3,994
Total cash and cash equivalents	$	75,015	$	—	$	—	$	75,015
Short-term investments
U.S. treasury securities		7,959		—		(2)		7,957
Corporate bonds		34,449		—		(9)		34,440
Commercial paper		61,116		—		(5)		61,111
Asset-backed securities		7,884		—		(1)		7,883
Total short-term investments	$	111,408	$	—	$	(17)	$	111,391
Total cash equivalents and investments	$	186,423	$	—	$	(17)	$	186,406


	December 31, 2017
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	5,882	$	—	$	—	$	5,882
Money market funds		68,651		—		—		68,651
Commercial paper		850		—		—		850
Total cash equivalents and investments	$	75,383	$	—	$	—	$	75,383
Short-term investments
U.S. treasury securities	$	3,994		—		(1)	$	3,993
Corporate bonds		26,853		—		(26)		26,827
Commercial paper		19,584		—		(14)		19,570
Asset-backed securities		8,209		—		(6)		8,203
Total short-term investments	$	58,640	$	—	$	(47)	$	58,593
Total cash equivalents and investments	$	134,023	$	—	$	(47)	$	133,976