Available-for-Sale Securities

3 Months Ended

Mar. 31, 2014

Available-for-Sale Securities

Available-for-Sale Securities

4. Available-for-Sale Securities

The classification of available-for-sale securities in the consolidated balance sheets is as follows:

(In thousands)	March 31, 2014		December 31, 2013
Cash and cash equivalents	$	119,160	$	125,009
Short-term investments	245,648		321,615
Marketable securities	59,831		55,374
Restricted cash	833		833
Total	$	425,472	$	502,831

The estimated fair value of available-for-sales securities is based on quoted market prices for these or similar investments that were based on prices obtained from a commercial pricing service. Available-for-sale securities are summarized below:

	March 31, 2014
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	37,042	$	74	$	—		$	37,116
U.S. government agencies	110,171		59		—			110,230
U.S. corporate notes	88,607		48		(10		)	88,645
U.S. commercial paper	74,487		—		—			74,487
Money market funds	114,994		—		—			114,994
Total	$	425,301	$	181	$	(10	)	$	425,472

	December 31, 2013
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	42,104	$	55	$	(1	)	$	42,158
U.S. government agencies	141,278		61		(8		)	141,331
U.S. corporate notes	94,923		54		—			94,977
U.S. commercial paper	102,021		2		(1		)	102,022
Money market funds	122,343		—		—			122,343
Total	$	502,669	$	172	$	(10	)	$	502,831

At March 31, 2014, all of the available-for-sale securities had contractual maturities within two years and the average duration of marketable securities was approximately seven months. We do not intend to sell the investments that are in an unrealized loss position, and it is unlikely that we will be required to sell the investments before recovery of their amortized cost basis, which may be maturity. We have determined that the gross unrealized losses on our marketable securities at March 31, 2104 were temporary in nature. All marketable securities with unrealized losses at March 31, 2014 have been in a loss position for less than twelve months.

During each of the three months ended March 31, 2014 and 2013, we sold available-for-sale securities totaling $5.0 million, and the related realized gains and losses were not significant in any of these periods.