Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 29, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 113,901	$ 157,381
Gross Unrealized Gains	203	307
Gross Unrealized Losses	(3)	(46)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Due in one year or less, Amortized Cost	28,994
Due after one year to five years, Amortized Cost	84,907
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Due in one year or less, Fair Value	29,059
Due after one year to five years, Fair Value	85,042
Fair Value	114,101	157,642
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,989	76,462
Gross Unrealized Gains	119	205
Gross Unrealized Losses	0	(4)
Fair Value	46,108	76,663
Agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	63,913	78,921
Gross Unrealized Gains	84	102
Gross Unrealized Losses	(3)	(42)
Fair Value	63,994	78,981
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,999	1,998
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 3,999	$ 1,998

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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