Investments (Tables)

3 Months Ended

Mar. 31, 2016

Investments, Debt and Equity Securities [Abstract]

Summary of Investments

Our investments consisted of the following (in thousands):

	As of March 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Short-term investment
Certificates of deposit	$	17,240	$	15	$	(1	)	$	17,254	$	17,254
Corporate notes and bonds	443,240		257		(247		)	443,250		443,250
U.S. Government agencies	285,609		41		(127		)	285,523		285,523
Total	$	746,089	$	313	$	(375	)	$	746,027	$	746,027

	As of December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Short-term investment
Certificates of deposit	$	19,160	$	—	$	(36	)	$	19,124	$	19,124
Corporate notes and bonds	448,688		—		(1,421		)	447,267		447,267
U.S. Government agencies	302,152		2		(770		)	301,384		301,384
Total	$	770,000	$	2	$	(2,227	)	$	767,775	$	767,775

Summary of Gross Unrealized Losses and Fair Value of Investments in a Continuous Unrealized Loss Position

The following tables present the gross unrealized losses and related fair values of our investments that have been in a continuous unrealized loss position (in thousands):

	As of March 31, 2016
	Less Than 12 Months					Greater Than 12 Months					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Certificates of deposit	$	1,159	$	(1	)	$	—	$	—		$	1,159	$	(1	)
Corporate notes and bonds	256,480		(234		)	15,974		(13		)	272,454		(247		)
U.S. Government agencies	156,623		(125		)	8,998		(2		)	165,621		(127		)
Total	$	414,262	$	(360	)	$	24,972	$	(15	)	$	439,234	$	(375	)

	As of December 31, 2015
	Less Than 12 Months					Greater Than 12 Months					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Certificates of deposit	$	18,404	$	(36	)	$	—	$	—		$	18,404	$	(36	)
Corporate notes and bonds	430,466		(1,407		)	16,801		(15		)	447,267		(1,422		)
U.S. Government agencies	266,541		(761		)	8,992		(8		)	275,533		(769		)
Total	$	715,411	$	(2,204	)	$	25,793	$	(23	)	$	741,204	$	(2,227	)

Summary of Contractual Maturities of Investments

The following table summarizes the contractual maturities of our investments at March 31, 2016 (in thousands):

	Amortized Cost		Fair Value
Due within one year	$	371,071	$	370,962
Due within one to two years	375,018		375,065
Total	$	746,089	$	746,027