Investments

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



	March 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	103,880	$	11	$	(14	)	$	103,877
Corporate notes and bonds	482,814		181		(395		)	482,600
Total available-for-sale securities	$	586,694	$	192	$	(409	)	$	586,477



	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

As of March 31, 2014, 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:



	March 31, 2014
Due in 1 year or less	$	317,842
Due in 1 year through 3 years	268,635
Total	$	586,477

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):



	March 31, 2014					December 31, 2013
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	41,465	$	(14	)	$	81,467	$	(21	)
Corporate notes and bonds	315,407		(395		)	293,642		(360		)
Total	$	356,872	$	(409	)	$	375,109	$	(381	)