Investments Continuous Unrealized Loss Position (Details) (USD $)	Sep. 29, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	$ 169,310,000	$ 153,346,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	28,508,000	29,613,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	59,000	72,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	28,508,000	29,613,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	59,000	72,000
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	169,302,000	153,328,000
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis	56,573,000	31,408,000
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value	56,586,000	31,396,000
Total, amortized cost basis	225,883,000	184,754,000
Total, fair value	225,888,000	184,724,000
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Total, fair value	17,997,000	9,996,000
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		1,440,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		1,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,440,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		1,000
Total, fair value	0	1,440,000
Securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	28,508,000	28,173,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	59,000	71,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	28,508,000	28,173,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	59,000	71,000
Total, fair value	$ 198,547,000	$ 162,669,000