Investments (Tables)

12 Months Ended

Dec. 31, 2011

Investments [Abstract]

Available-For-Sale Securities

	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
December 31, 2011
U.S. Treasury securities	$	228,001	$	24	$	(3	)	$	228,022
Corporate obligations		9,565		0		(1	)		9,564
Auction rate securities		5,780		0		0			5,780
Total	$	243,346	$	24	$	(4	)	$	243,366
Contractual Maturities
Due in one year or less	$	237,566						$	237,586
Due in 2017		5,780							5,780
Total	$	243,346						$	243,366
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
December 31, 2010
U.S. Treasury securities	$	249,580	$	10	$	(11	)	$	249,579
Corporate obligations		11,358		48		0			11,406
Auction rate securities		14,450		0		(1,419	)		13,031
Total	$	275,388	$	58	$	(1,430	)	$	274,016
Contractual Maturities
Due in one year or less	$	260,938						$	260,985
Due in 2017		14,450							13,031
Total	$	275,388						$	274,016

Schedule Of Investments

	December 31,
	2011		2010
Short-term investments	$	243,062	$	260,682
Long-term investments		0		13,031
Other non-current assets		304		303
Total	$	243,366	$	274,016

Estimated Fair Value Of Investments With Unrealized Losses

	Period of continuous unrealized loss
	12 Months or less					Greater than 12 months
	Fair value		Gross unrealized losses			Fair value		Gross unrealized losses
December 31, 2011
U.S. Treasury securities	$	80,234	$	(3	)	$	NA	$	NA
Corporate obligations		4,571		(1	)		NA		NA
Total	$	84,805	$	(4	)	$	NA	$	NA
December 31, 2010
U.S. Treasury securities	$	122,581	$	(11	)	$	NA	$	NA
Auction rate securities		NA		NA			13,031		(1,419	)
Total	$	122,581	$	(11	)	$	13,031	$	(1,419	)