Investments

The following is a summary of our investments (in thousands):



	December 31, 2013
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	124,330	$	10	$	(21	)	$	124,319
Corporate notes and bonds	399,519		129		(360		)	399,288
Total available-for-sale securities	$	523,849	$	139	$	(381	)	$	523,607



	December 31, 2012
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	72,850	$	—	$	(15	)	$	72,835
Corporate notes and bonds	158,038		8		(98		)	157,948
U.S. government agency securities	1,001		—		—			1,001
Total available-for-sale securities	$	231,889	$	8	$	(113	)	$	231,784

As of December 31, 2013, the contractual maturities of our investments did not exceed 24 months. The fair values of available-for-sale investments, by contractual maturity, are as follows:



	December 31, 2013
Due in 1 year or less	$	268,251
Due in 1 year through 3 years	255,356
Total	$	523,607

We had certain available-for-sale securities in a gross unrealized loss position, all of which had been in such position for less than twelve months. There were no impairments considered "other-than-temporary" as it is more likely than not we will hold the securities until maturity or a recovery of the cost basis. The following table shows the fair values and the gross unrealized losses of these available-for-sale securities aggregated by investment types (in thousands):



	December 31, 2013					December 31, 2012
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	81,467	$	(21	)	$	36,753	$	(15	)
Corporate notes and bonds	293,642		(360		)	137,558		(98		)
Total	$	375,109	$	(381	)	$	174,311	$	(113	)

As of December 31, 2013, we had a total of 122 available-for-sale securities in an unrealized loss position.