Marketable Securities

12 Months Ended

Dec. 31, 2011

Marketable Securities

Marketable Securities

4. Marketable Securities

        The following table is a summary of available-for-sale debt securities and money market funds recorded in cash equivalents or marketable securities in the Company's Consolidated Balance Sheets. Estimated fair values of available-for-sale securities are generally based on prices obtained from commercial pricing services:

	December 31, 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	$	66,150		$	24	$	—		$	66,174		$	25,966		$	10	$	—		$	25,976
U.S. government agencies		93,183			9		(17	)		93,175			54,625			30		(7	)		54,648
U.S. corporate notes		2,707			—		(2	)		2,705			34,695			9		(9	)		34,695
U.S. commercial paper		34,973			3		—			34,976			97,221			—		—			97,221
Money market funds		38,721			—		—			38,721			91,805			—		—			91,805
Total		235,734			36		(19	)		235,751			304,312			49		(16	)		304,345
Less amounts classified as cash equivalents		(38,721	)		—		—			(38,721	)		(157,151	)		—		—			(157,151	)
Less amounts classified as restricted cash		(893	)		—		—			(893	)		(893	)		—		—			(893	)
Amounts classified as marketable securities	$	196,120		$	36	$	(19	)	$	196,137		$	146,268		$	49	$	(16	)	$	146,301

        The following table provides the net realized gains (losses) on marketable securities for the periods presented:

	Year Ended December 31,
(in thousands)	2011			2010		2009
Realized gains	$	—		$	3	$	—
Realized losses		(2	)		—		—
Net realized gains (losses)	$	(2	)	$	3	$	—

        The Company realized no gains or losses in 2011 and 2010 that were previously classified as unrealized gains and losses in accumulated other comprehensive income at December 31, 2010 and 2009, respectively.

        The following table provides the breakdown of the marketable securities with unrealized losses at December 31, 2011:

	In loss position for less than 12 months					In loss position for more than 12 months				Total
(in thousands)	Fair Value		Estimated Gross Unrealized Losses			Fair Value		Estimated Gross Unrealized Losses		Fair Value		Estimated Gross Unrealized Losses
U.S. government agencies	$	47,807	$	(17	)	$	—	$	—	$	47,807	$	(17	)
U.S. corporate notes		2,754		(2	)		—		—		2,754		(2	)
Total	$	50,561	$	(19	)	$	—	$	—	$	50,561	$	(19	)

        At December 31, 2011, all of the available-for-sale debt securities had contractual maturities within twelve months and the average duration of marketable securities was approximately five 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 December 31, 2011 were temporary in nature.