AVAILABLE-FOR-SALE SECURITIES

6 Months Ended

Jun. 30, 2013

AVAILABLE-FOR-SALE SECURITIES

AVAILABLE-FOR-SALE SECURITIES

4. AVAILABLE-FOR-SALE SECURITIES

Securities classified as available-for-sale at June 30, 2013 and December 31, 2012 are summarized below. Estimated fair value is based on quoted market prices for these or similar investments that were based on prices obtained from a commercial pricing service:

	June 30, 2013
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	27,101	$	15	$	—		$	27,116
U.S. government agencies	157,932		48		(51		)	157,929
U.S. corporate notes	104,098		15		(42		)	104,071
U.S. commercial paper	44,967		—		—			44,967
Money market funds	192,694		—		—			192,694
Total	$	526,792	$	78	$	(93	)	$	526,777

	December 31, 2012
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	27,197	$	10	$	(2	)	$	27,205
U.S. government agencies	115,397		85		(16		)	115,466
U.S. corporate notes	91,544		32		(10		)	91,566
U.S. commercial paper	23,082		—		—			23,082
Money market funds	78,646		—		—			78,646
Total	$	335,866	$	127	$	(28	)	$	335,965

The following table summarizes the classification of the available-for-sale securities on the Company’s condensed consolidated balance sheets:

(in thousands)	June 31, 2013		December 31, 2012
Cash and cash equivalents	$	191,862	$	86,298
Short-term investments	243,768		153,640
Long-term marketable securities	90,314		95,194
Restricted cash	833		833
Total	$	526,777	$	335,965

At June 30, 2013, all of the marketable securities have contractual maturities within two years and the average duration of marketable securities was approximately nine months. The Company does not intend to sell the investments which are in an unrealized loss position and it is unlikely that the Company will be required to sell the investments before recovery of their amortized cost basis, which may be maturity. The Company has determined that the gross unrealized losses on its marketable securities at June 30, 2013, were temporary in nature. All marketable securities with unrealized losses have been in a loss position for less than twelve months.