Available-for-Sale Marketable Securities

9 Months Ended

Sep. 30, 2016

Investments, Debt and Equity Securities [Abstract]

Available-for-Sale Marketable Securities

3. Available-for-Sale Marketable Securities

As of September 30, 2016 and December 31, 2015, the Company’s available-for-sale marketable securities consisted of money market mutual funds 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 September 30, 2016 and December 31, 2015:

As of September 30, 2016

			Gross Unrealized
Type of Security	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market mutual funds	$	18,858	$	19	$	—		$	18,877
U.S. Treasury securities		2,501		1		—			2,502
U.S. government agency obligations		8,886		4		—			8,890
Corporate bonds		15,054		2		(5	)		15,051
Commercial paper		20,675		2		(3	)		20,674
Total available-for-sale marketable securities	$	65,974	$	28	$	(8	)	$	65,994

As of December 31, 2015

			Gross Unrealized
Type of Security	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market mutual funds	$	42,017	$	—	$	(31	)	$	41,986
U.S. Treasury securities		2,528		—		—			2,528
U.S. government agency obligations		13,492		4		—			13,496
Corporate bonds		14,194		—		(6	)		14,188
Commercial paper		19,444		1		(3	)		19,442
Total available-for-sale marketable securities	$	91,675	$	5	$	(40	)	$	91,640

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 September 30, 2016, the Company’s marketable debt securities mature at various dates through June 2017. The fair values and amortized cost 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 September 30, 2016				As of December 31, 2015
Contractual maturity	Fair Value		Amortized Cost		Fair Value		Amortized Cost
Less than one year	$	47,117	$	47,116	$	49,653	$	49,657

During the nine months ended September 30, 2016, the Company sold shares of money market mutual funds with a total fair value of $23,368 that were classified as available-for-sale marketable securities. The cost of the shares of money market mutual funds that were sold was determined by specific identification. Realized gains from those sales amounted to $12.

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.

	Less than 12 Months					12 Months or Greater				Total
As of September 30, 2016	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Corporate bonds	$	9,528	$	(5	)	$	—	$	—	$	9,528	$	(5	)
Commercial paper		9,443		(3	)		—		—		9,443		(3	)
Total	$	18,970	$	(8	)	$	—	$	—	$	18,970	$	(8	)
	Less than 12 Months					12 Months or Greater				Total
As of December 31, 2015	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Money market mutual funds	$	30,985	$	(31	)	$	—	$	—	$	30,985	$	(31	)
Corporate bonds		14,187		(6	)		—		—		14,187		(6	)
Commercial paper		11,960		(3	)		—		—		11,960		(3	)
Total	$	57,132	$	(40	)	$	—	$	—	$	57,132	$	(40	)

As of September 30, 2016 and December 31, 2015, the Company held a total of 20 out of 41 positions and 15 out of 23 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 September 30, 2016 and December 31, 2015. 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.