Marketable Securities

9 Months Ended

Sep. 30, 2017

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, 2017 and December 31, 2016 were as follows:

	September 30, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents
Commercial paper	$	7,999	$	—	$	(22	)	$	7,977
Short term investments
Commercial paper		54,275		—		(187	)		54,088
Corporate bonds		11,375		1		—			11,376
Total	$	73,649	$	1	$	(209	)	$	73,441

	December 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents
Commercial paper	$	59,175	$	2	$	(28	)	$	59,149
Corporate bonds		5,000		1		—			5,001
U.S. government agency bonds		5,500		—		—			5,500
Short term investments
Commercial paper		73,002		—		(214	)		72,788
Corporate bonds		11,089		4		(5	)		11,088
Total	$	153,766	$	7	$	(247	)	$	153,526

All of the Company’s marketable securities were classified as held-to-maturity investments and have maturities within one year of September 30, 2017. Approximately $80 million of the Company’s marketable securities matured during the nine months ended September 30, 2017, which was invested in money market funds as of September 30, 2017. See Note 13, Fair Value Measurement, for additional details.

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, 2017 and December 31, 2016 were as follows:

	September 30, 2017
	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		Unrealized  Loss		Estimated Fair Value		Unrealized Loss
	(in thousands)
Commercial paper	$	62,065	$	(209	)	$	—	$	—	$	62,065	$	(209	)
Total	$	62,065	$	(209	)	$	—	$	—	$	62,065	$	(209	)

	December 31, 2016
	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		Unrealized Loss		Estimated Fair Value		Unrealized Loss
	(in thousands)
Commercial paper	$	130,938	$	(242	)	$	—	$	—	$	130,938	$	(242	)
Corporate bonds		6,556		(5	)		—		—		6,556		(5	)
Total	$	137,494	$	(247	)	$	—	$	—	$	137,494	$	(247	)

The Company recognized interest income in general and administrative expenses within the condensed consolidated statements of operations during the three months ended September 30, 2017 and 2016 of $0.5 million and $0.4 million, respectively, and for the nine months ended September 30, 2017 and 2016 of $1.5 million and $0.9 million, respectively. During the three and nine months ended September 30, 2017 and 2016, 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).