Cash, Cash Equivalents and Investments (Details) (USD $) In Thousands, unless otherwise specified	Apr. 01, 2012	Dec. 31, 2011	Apr. 03, 2011	Dec. 31, 2010
Components of cash, cash equivalents and investments
Cash	$ 39,824	$ 36,404
Money market instruments	1,735	1,699
Cash and cash equivalents	41,559	38,103	37,014	33,203
Short-term investments	159,209	144,431
Limited partnership interest (accounted for using cost method)	5,933	5,933
Long-term investments	183,965	174,906
Total	384,733	357,440
Treasury bills [Member]
Components of cash, cash equivalents and investments
Short-term investments		1,945
Long-term investments	999
Municipal bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	57,862	54,036
Long-term investments	67,532	69,680
Corporate bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	61,517	55,570
Long-term investments	71,969	59,902
Agency bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	27,298	27,545
Long-term investments	13,987	12,335
Sovereign Bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	6,222	4,016
Long-term investments	18,279	22,355
Covered bonds [Member]
Components of cash, cash equivalents and investments
Short-term investments	4,443	1,319
Long-term investments	1,740	4,701
Asset-backed securities [Member]
Components of cash, cash equivalents and investments
Short-term investments	1,867
Long-term investments	$ 3,526