Cash, Cash Equivalents and Investments (Details 1) (USD $) In Thousands	Oct. 02, 2011	Dec. 31, 2010
Summary of available-for-sale investments
Amortized Cost	$ 310,248
Gross Unrealized Gains	715
Gross Unrealized Losses	(966)
Fair Value, Short-term investments	142,409	147,823
Fair Value, Total	309,997
Gross unrealized losses and fair value for available-for-sale investments
Fair Value, Less than 12 Months	107,062
Unrealized Losses, Less than 12 Months	(931)
Fair Value, 12 Months or Greater	27,942
Unrealized Losses, 12 Months or Greater	(35)
Fair Value	135,004
Unrealized Losses	(966)
Treasury bills [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	0	2,494
Municipal bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	49,626	75,457
Fair Value, Long-term investments	70,583	34,794
Fair Value, Total	120,209
Gross unrealized losses and fair value for available-for-sale investments
Fair Value, Less than 12 Months	31,230
Unrealized Losses, Less than 12 Months	(62)
Fair Value, 12 Months or Greater	704
Unrealized Losses, 12 Months or Greater	(1)
Fair Value	31,934
Unrealized Losses	(63)
Municipal bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	49,575
Gross Unrealized Gains	57
Gross Unrealized Losses	(6)
Fair Value, Short-term investments	49,626
Municipal bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	70,413
Gross Unrealized Gains	227
Gross Unrealized Losses	(57)
Corporate bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	60,123	34,543
Fair Value, Long-term investments	65,206	36,762
Fair Value, Total	125,329
Gross unrealized losses and fair value for available-for-sale investments
Fair Value, Less than 12 Months	56,169
Unrealized Losses, Less than 12 Months	(839)
Fair Value, 12 Months or Greater	18,630
Unrealized Losses, 12 Months or Greater	(25)
Fair Value	74,799
Unrealized Losses	(864)
Corporate bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	60,879
Gross Unrealized Gains	9
Gross Unrealized Losses	(765)
Fair Value, Short-term investments	60,123
Corporate bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	65,143
Gross Unrealized Gains	162
Gross Unrealized Losses	(99)
Agency bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	31,276	15,979
Fair Value, Long-term investments	13,894	21,025
Fair Value, Total	45,170
Gross unrealized losses and fair value for available-for-sale investments
Fair Value, Less than 12 Months	19,663
Unrealized Losses, Less than 12 Months	(30)
Fair Value, 12 Months or Greater	8,608
Unrealized Losses, 12 Months or Greater	(9)
Fair Value	28,271
Unrealized Losses	(39)
Agency bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	31,289
Gross Unrealized Gains	15
Gross Unrealized Losses	(28)
Fair Value, Short-term investments	31,276
Agency bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	13,878
Gross Unrealized Gains	27
Gross Unrealized Losses	(11)
Sovereign debt [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	0	19,350
Fair Value, Long-term investments	12,971	0
Fair Value, Total	12,971
Sovereign debt [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	12,768
Gross Unrealized Gains	203
Covered bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	1,384	0
Fair Value, Long-term investments	4,934	3,541
Fair Value, Total	6,318
Covered bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	1,384
Fair Value, Short-term investments	1,384
Covered bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	4,919
Gross Unrealized Gains	$ 15