Marketable Securities

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

As of June 30, 2018 and December 31, 2017 the fair value of available-for-sale marketable securities by type of security was as follows:

	June 30, 2018
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper		12,938		—		—			12,938
U.S. government obligations	$	64,310	$	2	$	(89	)	$	64,223
Corporate bonds		88,897		—		(226	)		88,671
	$	166,145	$	2	$	(315	)	$	165,832

	December 31, 2017
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper	$	22,436	$	—	$	—		$	22,436
U.S. government obligations		121,470	$	—		(136	)		121,334
Corporate bonds		152,630	$	—		(273	)		152,357
	$	296,536	$	—	$	(409	)	$	296,127

As of June 30, 2018 and December 31, 2017, marketable securities consisted of approximately $165.8 and $264.6 million, respectively, of investments that mature within twelve months. As of December 31, 2017, long-term investments consisted of approximately $31.5 million of investments that mature after one year but within two years or less from the balance sheet date. There were no investments with maturities greater than twelve months as of June 30, 2018.