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

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	)

Unrealized losses related to these investments are due to interest rate fluctuations as opposed to credit quality. In addition, we do not intend to sell, and it is not more likely than not that we would be required to sell, these investments before recovery of their cost basis. As a result, there is no other-than-temporary impairment for these investments as of March 31, 2016 and December 31, 2015.

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

All available-for-sale securities have been classified as current, based on management's intent and ability to use the funds in current operations.

During 2015, we invested in a privately held company, obtaining an initial 12.5% ownership interest. This investment is accounted for under the equity method based on our ability to exercise significant influence over operating and financial policies of the investee, and is classified within deposits and other long-term assets on our condensed consolidated balance sheets. The carrying value of this investment was $1.6 million and $1.8 million as of March 31, 2016 and December 31, 2015, respectively.