Marketable Securities

3 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

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

	March 31, 2018
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper		22,383		—		—			22,383
U.S. government obligations	$	84,254	$	—	$	(156	)	$	84,098
Corporate bonds		123,218		—		(423	)		122,795
	$	229,855	$	—	$	(579	)	$	229,276

	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 March 31, 2018 and December 31, 2017, marketable securities consisted of approximately $224.3 and $264.6 million, respectively, of investments that mature within twelve months and approximately $4.9 million and $31.5 million, respectively of investments that mature after one year but within two years or less from the balance sheet date.