Available-for-Sale Securities

9 Months Ended

Sep. 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:

	September 30, 2012
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	30,233	$	9	$	—		$	30,242
U.S. government agencies	107,073		69		(1		)	107,141
U.S. corporate notes	98,599		45		(7		)	98,637
U.S. commercial paper	37,336		1		—			37,337
Money market funds	85,634		—		—			85,634
Total	$	358,875	$	124	$	(8	)	$	358,991

	December 31, 2011
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	66,150	$	24	$	—		$	66,174
U.S. government agencies	93,183		9		(17		)	93,175
U.S. corporate notes	2,707		—		(2		)	2,705
U.S. commercial paper	34,973		3		—			34,976
Money market funds	38,721		—		—			38,721
Total	$	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)	September 30, 2012		December 31, 2011
Cash and cash equivalents	$	107,987	$	38,721
Short-term investments	161,209		196,137
Long-term marketable securities	88,962		—
Restricted cash	833		893
Total	$	358,991	$	235,751

At September 30, 2012, 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 September 30, 2012, were temporary in nature. All marketable securities with unrealized losses have been in a loss position for less than twelve months.