A summary of cash, cash equivalents and available-for-sale marketable securities held by the Company as of September 30, 2018 and December 31, 2017 is as follows (in thousands):


	September 30, 2018
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value

Cash and cash equivalents:
Cash (Level 1)	$	2,127	$	—	$	—	$	2,127
Money market funds (Level 1)		35,919		—		—		35,919
Corporate debt securities due within 3 months of date of purchase (Level 2)		—		—		—		—
Total cash and cash equivalents		38,046		—		—		38,046
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		437,106		13		(144)		436,975
Corporate debt securities due between 1 and 2 years of the date of purchase (Level 2)		13,529		—		(12)		13,517
Total cash, cash equivalents and marketable securities	$	488,681	$	13	$	(156)	$	488,538


	December 31, 2017
			Unrealized		Unrealized		Fair
	Cost		Gains		losses		value

Cash and cash equivalents:
Cash (Level 1)	$	2,725	$	—	$	—	$	2,725
Money market funds (Level 1)		145,902		—		—		145,902
Corporate debt securities due within 3 months of date of purchase (Level 2)		—		—		—		—
Total cash and cash equivalents		148,627		—		—		148,627
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		42,931		—		(31)		42,900
Total cash, cash equivalents and marketable securities	$	191,558	$	—	$	(31)	$	191,527