Short-Term Investments (Tables)

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-sale Securities

Our investments in debt and equity securities classified as available-for-sale consisted of the following (in thousands):

	As of December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
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

	As of December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
Certificates of deposit	$	5,000	—		$	(6	)	$	4,994	$	—	$	4,994
Corporate notes and bonds	143,215		4		(235		)	142,984		—		142,984
U.S. Government agencies	121,021		1		(205		)	120,817		12,950		107,867
Total	$	269,236	$	5	$	(446	)	$	268,795	$	12,950	$	255,845

Summary of Unrealized Losses on Investments

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

	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	)

	As of December 31, 2014
	Less Than 12 Months					Greater Than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Certificates of deposit	$	3,793	$	(6	)	$	—	$	—	$	3,793	$	(6	)
Corporate notes and bonds	130,920		(235		)	—		—		130,920		(235		)
U.S. Government agencies	109,868		(205		)	—		—		109,868		(205		)
Total	$	244,581	$	(446	)	$	—	$	—	$	244,581	$	(446	)

Summary of Contractual Maturities

The following table summarizes the contractual maturities of these investments at December 31, 2015 (in thousands):

	Amortized Cost		Fair Value
Due within one year	$	384,370	$	383,858
Due within one to two years	385,630		383,917
Total	$	770,000	$	767,775