Available-for-Sale Securities

6 Months Ended

Jun. 30, 2012

Available-for-Sale Securities

Available-for-Sale Securities

4. Available-for-Sale Securities

The following table is a summary of available-for-sale debt securities recorded in cash and cash equivalents, short-term investments, long-term marketable securities, or restricted cash in the Company’s condensed consolidated balance sheets. Estimated fair values of available-for-sale securities are generally based on prices obtained from commercial pricing services:

	June 30, 2012									December 31, 2011
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	30,270	$	1	$	(16	)	$	30,255	$	66,150	$	24	$	—		$	66,174
U.S. government agencies	112,266		4		(74		)	112,196		93,183		9		(17		)	93,175
U.S. corporate notes	60,176		9		(33		)	60,152		2,707		—		(2		)	2,705
U.S. commercial paper	44,993		—		—			44,993		34,973		3		—			34,976
Money market funds	129,891		—		—			129,891		38,721		—		—			38,721
Total	$	377,596	$	14	$	(123	)	$	377,487	$	235,734	$	36	$	(19	)	$	235,751

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

(in thousands)	June 30, 2012		December 31, 2011
Cash and cash equivalents	$	159,053	$	38,721
Short-term investments	134,393		196,137
Long-term marketable securities	83,208		—
Restricted cash	833		893
Total	$	377,487	$	235,751

At June 30, 2012, all of the marketable securities have contractual maturities within twenty-four months and the average duration of marketable securities was approximately eleven 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, 2012, were temporary in nature. All marketable securities with unrealized losses have been in a loss position for less than twelve months.