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


	June 30, 2018
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	2,932		—		—	$	2,932
Money market funds		67,611		—		—		67,611
Corporate bonds		2,664				—		2,664
Commercial paper		18,544		—		—		18,544
Total cash and cash equivalents	$	91,751	$	—	$	—	$	91,751
Short-term investments
U.S. treasury securities		8,459		1		—		8,460
Corporate bonds		38,788		—		(31)		38,757
Commercial paper		64,642		—		(2)		64,640
Asset-backed securities		9,126		—		(3)		9,123
Total short-term investments	$	121,015	$	1	$	(36)	$	120,980
Total cash equivalents and investments	$	212,766	$	1	$	(36)	$	212,731


	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