Cash, Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments and Cash [Abstract]

Schedule of reconciliation of cash, cash equivalents and marketable securities from amortized cost to fair value

The following tables summarize the Company's cash, cash equivalents and marketable securities as of December 31, 2017 and 2016 (in thousands):

As of December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Cash, money market funds and overnight repurchase agreements	$	73,651	$	—	$	—		$	73,651
U.S. government-sponsored enterprise securities due in one year or less	18,186		—		(5		)	18,181
Corporate debt securities due in one year or less	118,541		3		(115		)	118,429
Corporate debt securities due in more than one year	30,487		1		(43		)	30,445
Certificates of deposit due in one year or less	6,501		—		—			6,501
Certificates of deposit due in more than one year	1,297		—		(4		)	1,293
Commercial paper obligations due in one year or less	108,573		65		(8		)	108,630
Asset-backed securities due in one year or less	17,307		—		(30		)	17,277
Asset-backed securities due in more than one year	5,487		—		(4		)	5,483
Total	$	380,030	$	69	$	(209	)	$	379,890
Reported as:
Cash and cash equivalents	$	73,651	$	—	$	—		$	73,651
Marketable securities	306,379		69		(209		)	306,239
Total	$	380,030	$	69	$	(209	)	$	379,890

As of December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Cash, money market funds and overnight repurchase agreements	$	150,738	$	—	$	—		$	150,738
Corporate debt securities due in one year or less	47,942		—		(36		)	47,906
Commercial paper obligations due in one year or less	84,301		135		—			84,436
Asset-backed securities due in one year or less	70,084		1		(14		)	70,071
Total	$	353,065	$	136	$	(50	)	$	353,151
Reported as:
Cash and cash equivalents	$	150,738	$	—	$	—		$	150,738
Marketable securities	202,327		136		(50		)	202,413
Total	$	353,065	$	136	$	(50	)	$	353,151