Investments (Tables)

6 Months Ended

Jun. 30, 2016

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-sale Securities

The amortized cost, gross unrealized gains, gross unrealized losses, and fair value of available-for-sale investment securities by major security type and class of security at June 30, 2016 and December 31, 2015 were as follows:

		Investments
(In thousands)		Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
2016
	Federal agency notes	$	279,850	$	259	$	(46	)	$	280,063
	Commercial paper	31,935		39		—			31,974
	Subtotal	311,785		298		(46		)	312,037
	Mutual funds	704		274		—			978
	Total	$	312,489	$	572	$	(46	)	$	313,015
2015
	Federal agency notes	$	285,276	$	—	$	(519	)	$	284,757
	Commercial paper	31,730		—		(58		)	31,672
	Subtotal	317,006		—		(577		)	316,429
	Mutual funds	482		261		—			743
	Total	$	317,488	$	261	$	(577	)	$	317,172

Schedule of Maturities of Available-for-sale Securities

The maturities of available-for-sale securities at June 30, 2016 were as follows:

(In thousands)	Amortized cost		Fair value
Federal agency notes
Due in one year or less	$	214,745	$	214,821
Due after one year through two years	65,105		65,242
Total	$	279,850	$	280,063
Commercial paper
Due in one year or less	$	16,485	$	16,488
Due after one year through two years	15,450		15,486
Total	$	31,935	$	31,974