Cash, Cash Equivalents and Investments (Details) (USD $)	Jul. 01, 2012	Dec. 31, 2011	Jul. 03, 2011	Dec. 31, 2010
Components of cash, cash equivalents and investments
Cash	$ 25,422,000	$ 36,404,000
Cash equivalents	134,016,000
Money market instruments	46,554,000	1,699,000
Cash and cash equivalents	205,992,000	38,103,000	42,676,000	33,203,000
Short-term investments	59,943,000	144,431,000
Limited partnership interest (accounted for using cost method)	5,562,000	5,933,000
Long-term investments	124,748,000	174,906,000
Total	390,683,000	357,440,000
Treasury bills [Member]
Components of cash, cash equivalents and investments
Short-term investments		1,945,000
Municipal bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	39,827,000	54,036,000
Long-term investments	82,866,000	69,680,000
Corporate bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	18,162,000	55,570,000
Long-term investments	27,897,000	59,902,000
Corporate stock [Member]
Components of cash, cash equivalents and investments
Short-term investments	353,000
Agency bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments		27,545,000
Long-term investments	1,001,000	12,335,000
Sovereign Bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments		4,016,000
Long-term investments	3,882,000	22,355,000
Covered bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments		1,319,000
Long-term investments		4,701,000
Asset-backed securities [Member]
Components of cash, cash equivalents and investments
Short-term investments	1,601,000
Long-term investments	$ 3,540,000