Marketable Securities

9 Months Ended

Sep. 30, 2016

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

The amortized cost, unrealized gains and losses and estimated fair value of the Company’s held-to-maturity marketable securities as of September 30, 2016 and December 31, 2015 were as follows:

	September 30, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents
Commercial paper	$	35,871	$	—	$	(21	)	$	35,850
Short term investments
Commercial paper		100,652		—		(219	)		100,433
Corporate bonds		18,091		4		(1	)		18,094
Total	$	154,614	$	4	$	(241	)	$	154,377

	December 31, 2015
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents
Commercial paper	$	22,744	$	—	$	(5	)	$	22,739
Short term investments
Commercial paper		90,949		—		(102	)		90,847
Corporate bonds		41,503		9		(39	)		41,473
U.S. government agency bonds		8,996		8		—			9,004
Total	$	164,192	$	17	$	(146	)	$	164,063

All of the Company’s marketable securities were classified as held-to-maturity investments and have maturities within one year of September 30, 2016.

The gross unrealized losses, estimated fair value and length of time the individual marketable securities were in a continuous loss position for those marketable securities in an unrealized loss position as of September 30, 2016 and December 31, 2015 were as follows:

	September 30, 2016
	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		UnrealizedLoss		Estimated Fair Value		Unrealized Loss
	(in thousands)
Commercial paper	$	136,283	$	(240	)	$	—	$	—	$	136,283	$	(240	)
Corporate bonds		4,882		(1	)		—		—		4,882		(1	)
Total	$	141,165	$	(241	)	$	—	$	—	$	141,165	$	(241	)

	December 31, 2015
	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		UnrealizedLoss		Estimated Fair Value		Unrealized Loss
	(in thousands)
Commercial paper	$	113,586	$	(107	)	$	—	$	—	$	113,586	$	(107	)
Corporate bonds		31,952		(39	)		—		—		31,952		(39	)
Total	$	145,538	$	(146	)	$	—	$	—	$	145,538	$	(146	)

During the three and nine months ended September 30, 2016 and 2015, the Company did not recognize any other-than-temporary impairment losses related to its marketable securities.

The Company’s marketable securities are classified within Level 2 of the fair value hierarchy (see Note 13, Fair Value Measurement, for further details).