Marketable Securities

6 Months Ended

Jun. 30, 2011

Marketable Securities

Marketable Securities

5.  Marketable Securities

The Company manages, monitors and measures its investments in highly liquid investment grade securities by major security type. Investments in debt securities are accounted for as available-for-sale securities, carried at fair value with unrealized gains and losses reported in accumulated other comprehensive income (loss), held for use in current operations and classified in current assets as marketable securities. The cost of securities sold is based on the specific-identification method.

The estimated fair value amounts were determined using available market information. Available-for-sale debt securities recorded in cash equivalents, marketable securities or restricted cash in the Company’s condensed consolidated balance sheets were as follows:

	June 30, 2011											December 31, 2010
(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	$	66,496		$	28	$	(6	)	$	66,518		$	25,966		$	10	$	—		$	25,976
U.S. government agencies	77,717			18		(39		)	77,696			54,625			30		(7		)	54,648
U.S. corporate notes	21,100			1		(10		)	21,091			34,695			9		(9		)	34,695
U.S. commercial paper	44,356			—		—			44,356			97,221			—		—			97,221
Money market funds	72,393			—		—			72,393			91,805			—		—			91,805
Total	282,062			47		(55		)	282,054			304,312			49		(16		)	304,345
Less amounts classified as cash equivalents	(87,932		)	—		—			(87,932		)	(157,151		)	—		—			(157,151		)
Less amounts classified as restricted cash	(893		)	—		—			(893		)	(893		)	—		—			(893		)
Amounts classified as marketable securities	$	193,237		$	47	$	(55	)	$	193,229		$	146,268		$	49	$	(16	)	$	146,301

At June 30, 2011, all of the marketable securities had contractual maturities within twelve months and the average duration of marketable securities was approximately seven 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, 2011 were temporary in nature. All marketable securities with unrealized losses have been in a loss position for less than twelve months.