Investments (Tables)

6 Months Ended

Jun. 30, 2017

Available-for-sale Securities [Abstract]

Summary of Investments

The following is a summary of our available-for-sale investment securities, excluding those securities classified within cash and cash equivalents on the condensed consolidated balance sheets (in thousands):

	June 30, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	68,075	$	—	$	—		$	68,075
Corporate notes and bonds	656,402		123		(878		)	655,647
Certificates of deposit	36,389		—		—			36,389
U.S. government agency securities	56,323		—		(134		)	56,189
Marketable equity securities	10,000		12,214		—			22,214
Total available-for-sale securities	$	827,189	$	12,337	$	(1,012	)	$	838,514

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	56,839	$	—	$	—		$	56,839
Corporate notes and bonds	628,054		91		(1,590		)	626,555
Certificates of deposit	35,355		—		—			35,355
U.S. government agency securities	42,088		7		(62		)	42,033
Total available-for-sale securities	$	762,336	$	98	$	(1,652	)	$	760,782

Investments Classified by Contractual Maturity Date

The fair values of these securities, by remaining contractual maturity, are as follows (in thousands):

	June 30, 2017
Due in 1 year or less	$	496,505
Due in 1 to 2 years	319,795
Total	$	816,300

Fair Values and Gross Unrealized Losses of Available-for-Sale Securities Aggregated by Investment Category

The following table shows the fair values and the gross unrealized losses of our available-for-sale investment securities, classified by the length of time that the securities have been in a continuous unrealized loss position, and aggregated by investment types (in thousands): 

	June 30, 2017
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate notes and bonds	$	511,868	$	(877	)	$	3,775	$	(1	)	$	515,643	$	(878	)
U.S. government agency securities	65,175		(134		)	—		—			65,175		(134		)
Total	$	577,043	$	(1,011	)	$	3,775	$	(1	)	$	580,818	$	(1,012	)

	December 31, 2016
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate notes and bonds	$	492,503	$	(1,530	)	$	47,940	$	(60	)	$	540,443	$	(1,590	)
U.S. government agency securities	30,033		(62		)	—		—			30,033		(62		)
Total	$	522,536	$	(1,592	)	$	47,940	$	(60	)	$	570,476	$	(1,652	)