Fair Value (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 29, 2012	Dec. 31, 2011
Summary of available-for-sale securities
Amortized Cost	$ 85,295	$ 70,819
Gross Unrealized Gains	73	56
Gross Unrealized Losses	(13)	(21)
Total short-term investments	85,355	70,854
State, municipal and local government agencies bonds [Member]
Summary of available-for-sale securities
Amortized Cost	44,609	38,785
Gross Unrealized Gains	67	46
Gross Unrealized Losses	(5)	(6)
Total short-term investments	44,671	38,825
Corporate bonds [Member]
Summary of available-for-sale securities
Amortized Cost	22,514	18,613
Gross Unrealized Gains	6	6
Gross Unrealized Losses	(7)	(15)
Total short-term investments	22,513	18,604
U.S. federal government bonds [Member]
Summary of available-for-sale securities
Amortized Cost	5,786	9,226
Gross Unrealized Gains		4
Gross Unrealized Losses	(1)
Total short-term investments	5,785	9,230
Commercial paper [Member]
Summary of available-for-sale securities
Amortized Cost	12,386	4,195
Total short-term investments	$ 12,386	$ 4,195