Cash, Cash Equivalents and Investments (Details 1) (USD $)	Jul. 01, 2012	Dec. 31, 2011
Summary of available-for-sale investments
Amortized Cost	$ 177,967,000
Gross Unrealized Gains	834,000
Gross Unrealized Losses	(25,000)
Fair Value, Short-term investments	59,943,000	144,431,000
Fair Value, Total	178,776,000
Municipal bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	39,827,000	54,036,000
Fair Value, Long-term investments	82,866,000	69,680,000
Fair Value, Total	122,693,000
Municipal bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	39,787,000
Gross Unrealized Gains	44,000
Gross Unrealized Losses	(4,000)
Municipal bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	82,535,000
Gross Unrealized Gains	352,000
Gross Unrealized Losses	(21,000)
Corporate bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	18,162,000	55,570,000
Fair Value, Long-term investments	27,897,000	59,902,000
Fair Value, Total	46,059,000
Corporate bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	18,123,000
Gross Unrealized Gains	39,000
Corporate bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	27,631,000
Gross Unrealized Gains	266,000
Agency bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments		27,545,000
Fair Value, Long-term investments	1,001,000	12,335,000
Fair Value, Total	1,001,000
Agency bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	1,000,000
Gross Unrealized Gains	1,000
Sovereign Bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments		4,016,000
Fair Value, Long-term investments	3,882,000	22,355,000
Fair Value, Total	3,882,000
Sovereign Bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	3,771,000
Gross Unrealized Gains	111,000
Covered bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments		1,319,000
Fair Value, Long-term investments		4,701,000
Asset-backed securities [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	1,601,000
Fair Value, Long-term investments	3,540,000
Fair Value, Total	5,141,000
Asset-backed securities [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	1,600,000
Gross Unrealized Gains	1,000
Asset-backed securities [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	3,520,000
Gross Unrealized Gains	$ 20,000