3. Available-for-Sale Marketable Securities

As of June 30, 2017 and December 31, 2016, the Company’s available-for-sale marketable securities consisted of a money market fund and debt securities issued by the U.S. government and government-sponsored entities and by investment grade institutions.

The following tables summarize the Company’s available-for-sale marketable securities by major type of security as of June 30, 2017 and December 31, 2016:

As of June 30, 2017


			Gross Unrealized					Estimated Fair Value
Type of Security	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	$	42,976	$	7	$	—		$	42,983
U.S. government agency obligations		7,999		—		(1	)		7,998
Corporate bonds		26,901		—		(12	)		26,889
Commercial paper		25,157		—		(7	)		25,150

Total available-for-sale marketable securities	$	103,033	$	7	$	(20	)	$	103,020

As of December 31, 2016


			Gross Unrealized					Estimated Fair Value
Type of Security	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	$	8,268	$	8	$	—		$	8,276
U.S. Treasury securities		2,523		—		(1	)		2,522
U.S. government agency obligations		3,501		1		—			3,502
Corporate bonds		16,683		—		(6	)		16,677
Commercial paper		15,206		3		(2	)		15,207

Total available-for-sale marketable securities	$	46,181	$	12	$	(9	)	$	46,184

All available-for-sale marketable securities are classified in the Company’s Condensed Balance Sheets as Marketable securities.

The Company classifies its marketable debt securities based on their contractual maturity dates. As of June 30, 2017, the Company’s marketable debt securities mature at various dates through April 2018. The amortized cost and fair values of marketable debt securities by contractual maturity were as follows. The table does not include money market funds that are classified as available-for-sale marketable securities.


	As of June 30, 2017				As of December 31, 2016
Contractual maturity	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than one year	$	60,057	$	60,037	$	37,913	$	37,908

During the six months ended June 30, 2017, the Company sold shares of two investments in commercial paper before their respective maturity dates and shares in a money market fund with a total fair value of $5,430 that were all classified as available-for-sale marketable securities. The cost of the shares of commercial paper and the money market fund that were sold was determined by specific identification. The sales of the investments in commercial paper as well as the sale of the shares of the money market fund each resulted in realized gains, totaling $3.

The following tables show the fair value of the Company’s available-for-sale marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual investments have been in a continuous unrealized loss position.

As of June 30, 2017


	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. government agency obligations	$	4,004	$	(1	)	$	—	$	—	$	4,004	$	(1	)
Corporate bonds		24,888		(12	)		—		—		24,888		(12	)
Commercial paper		22,152		(7	)		—		—		22,152		(7	)

Total	$	51,044	$	(20	)	$	—	$	—	$	51,044	$	(20	)

As of December 31, 2016


	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. Treasury securities	$	2,522	$	(1	)	$	—	$	—	$	2,522	$	(1	)
Corporate bonds		9,919		(6	)		—		—		9,919		(6	)
Commercial paper		5,227		(2	)		—		—		5,227		(2	)

Total	$	17,668	$	(9	)	$	—	$	—	$	17,668	$	(9	)

As of June 30, 2017 and December 31, 2016, the Company held a total of 28 out of 33 positions and 18 out of 34 positions, respectively, that were in an unrealized loss position, none of which had been in an unrealized loss position for 12 months or greater. Based on the Company’s review of these securities, the Company believes that the cost basis of its available-for-sale marketable securities is recoverable and that, therefore, it had no other-than-temporary impairments on these securities as of June 30, 2017 and December 31, 2016. The Company does not intend to sell these debt securities and the Company believes it is not more likely than not that it will be required to sell these securities before the recovery of their amortized cost basis, which may be maturity.