Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security

As of June 30, 2017 and December 31, 2016 the fair value of available-for-sale marketable securities by type of security was as follows:

	June 30, 2017
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. government obligations	$	46,475	$	—	$	(9	)	$	46,466
Commercial paper		14,445		—		—			14,445
Corporate bonds		101,837		3		(71	)		101,769
	$	162,757	$	3	$	(80	)	$	162,680

	December 31, 2016
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper	$	7,769	$	—	$	—		$	7,769
U.S. government obligations		75,524		5		(12	)		75,517
Corporate bonds		96,193		1		(66	)		96,128
	$	179,486	$	6	$	(78	)	$	179,414